Stopping Barrel Fall At Linkdown

Stopping Barrel Fall At Linkdown

Much is written about what should arrest the barrel's downward movement at linkdown. Some say the VIS in conjunction with the link in compression with no contact with the receiver bed. Others say by the receiver bed alone with no compressive force on the link.

Based on Ordnance Dept. blueprint spec's it seems a vast majority of GI M1911A1's assembled with in-tolerance parts would have the barrel stopped by receiver bed contact.

This conclusion was based on determining what "size" link would be needed to halt the barrel's downward motion by contact with both the bed and the VIS, with the link just starting to get compressed. A slightly longer link would prevent barrel/bed contact and thus stop the barrel by link compression/VIS contact. A slightly shorter link could never be in compression and thus rely on bed contact to do the stopping.

Note: "Size", as used here, refers to the distance between the edges of the link holes [ O(size)O ] - not their centers.

The only assumptions made were: barrel bore axis was parallel to the receiver top at linkdown; barrel link pin diameter equalled the feet hole diameters for a press fit.

Calculations (lots of 'em!) led to 0.1056 +/- 0.0102 inch as the "size" needed to stop barrel downward movement by both the VIS and the bed. With no specification available for the link, a new, unused Colt standard "0.278" link was measured and its "size" was 0.097 inch. In a mid-spec GI M1911A1, this link is almost 0.009 inch short of allowing stoppage by both the VIS and bed, could therefore never be in compression, and would thus cause the barrel's fall to be halted by the bed.

Don't know what JMB's intention was for this, but it seems (to me at least) that most GI M1911A1's assembled with in-spec barrels, barrel link pins, links, slide stop pins and receivers would stop the fall of their barrels by contact with the receiver bed - and their links would be loose at linkdown.

If all this is close to being correct, why all the fuss about avoiding barrel/bed contact? Was JMB wrong? Or, does it really make any difference how the barrel's fall is stopped?

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If all this is close to being correct, why all the fuss about avoiding barrel/bed contact? Was JMB wrong? Or, does it really make any difference how the barrel's fall is stopped?

No. JMB wasn't wrong. The barrel should be stopped a thousandth or two off the bed, but most pistols born after about 1937 do stop on the bed. The trick is not to let them hit the bed first, before the barrel's rearward movement has been stopped by the VIS. Once the barrel has stopped, it can freefall onto the bed without problems.

It's when it hits the bed while still moving that bad things happen.

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Others say by the receiver bed alone with no compressive force on the link.

Niemi, could you be more specific about just who has said this??

Second thought: You say that link selection is done to determine how to properly halt the barrel in linkdown. I don't believe this is completely correct. While link length does affect how the barrel stops, the link length (these days) is selected based on the position of the lower lugs when the barrel is fully in battery. Given a particular gun with its own unique vertical stacking dimensions, you will select a link that allows the slide stop to support the lower barrel lugs in battery.

The receiver bed? Think I've seen that in one of Kuhnhausen's manuals.

Hi Lazarus: The answer to your question;

Ken Hallock, on page 126 of his book, Hallock's .45 Auto Handbook. In his description of how to check if the link is too long he says the barrel should seat firmly into the curvature in front of the feed ramp (bed) when pushed down and back, and the slide stop should not be under any pressure from the link and be free to move.

Regarding your "second thought", I agree with you completely. My apologies if I implied I was going to use any of my findings to select a link to allow a certain linkdown condition. My aim was simply to determine how a mid-spec GI M1911 halted the fall of its barrel, and the link's hole edge separation was the simplest way I could find to make that determination.

OK, then.

Suprising what you can find these days. Kind of like that guy who thinks his recoil spring somehow affects the trigger pull. I have a copy of book, currently sold by Brownells and others, who advocates the removal the extractor's middle "hump". He states that it is only there to make it easier for production line guns to get a working extractor. The "real" method involves removing it and using his special adjustment technique. Fortunately, this suggestion is not widely distributed on the 1911 forums.

LOL. And I once read, in a shooting magazine, that a lighter weight pistol would permit the shooter to feel less recoil since, if I recall his goofy logic, there was less mass to hit your hand. I kid you not.

Laz... While I don't remove the outboard dogknot, I reduce its size by about .015 inch on most installations. It lets me put a little more bend in the stem without making the extractor so stiff and unyielding on the front half... and it gives the extractor a little more wiggle room when the channel gets all canked up... AND... it allows the hook to snap over the rim easier in case the round happens to push-feed. I guess I've added yet another redundancy to the system.

Works well, but usually requires a fitted firing pin stop to keep it from clocking.

Hi (again) Lazarus: Here's another writer who calls for the barrel to seat on the receiver bed; Mike Watkins (Brownell's) in the 17th paragraph of "Building A 1911 - Part III" in the Technical Issues section of the Gunsmithing part of this forum.

Iron Bottom, in Post #5 this thread, thinks he saw it one of Kuenhausen's books. Don't have any of J.K.'s books (yet), so I really can't say.

FWIW:my simplistic thinking on this subject is it'd be best to stop the downward movement by barrel/bed contact. These two surfaces would seem to be able to withstand the impact - however much impact there is - a lot better than having the link transfer it all to the slide stop pin and its holes in the receiver.

Tuner, in Post #2 this thread, says it's OK for the barrel to contact the bed as long as its rearward motion has already been halted by the VIS. How can I tell if the barrel contacts the VIS before it contacts the bed when the gun is fired?

In Kuhnhausen's Vol 1, page 65 under Mating Check and page 66 under Bottom Lug Rear Adjustment, there are these procedures for barrel and link fitting. Reads, to me, like the barrel lower lug should not contact the frame. Sure would simplify things to only have to remove a little material from the rear of the lower barrel lug. Getting the barrel to stop on the lug .001 above the frame is a delicate operation. But Tuner as well as Shuemann recommend stopping the barrel on the lug and VIS and it is hard to argue with their reasons.

Hi Iron Bottom: After reading through Shuemann's materials several times it occured to me that (as a maker of barrels) he'd be naturally reluctant to instruct the general buying public to remove metal from the aft vertical surfaces of the barrel's feet. This cuz if not properly done, and the radius at the top is removed by an uninformed "filer", a good starting point for a crack at the feet/chamber junction will have been created by the sharp corner.

Shuemann's instruction to move the VIS aft seems a poor choice to me for another reason. Why diddle with the VIS in the receiver (the most expensive part and perhaps the longest lasting part) to make the barrel fit, when the next barrel that gets installed may be some other brand. Could be the VIS might need to get moved forward to properly fit this barrel, and the shade tree gun plumber is in a real predicament.

Moving a VIS back is difficult enough, but moving it forward would involve (I think) welding it up and then having to dress the weldment back to fit!

I also think of the consequences of messing up what I'm working on: do I want to mess up a barrel or a receiver?

Well, for one thing, I have had several conversations with Wil Shuemann and I do not think he would give anyone misleading information. The next barrel? I'm sixty years old. I don't worry about the next barrel. Or frame.

Hi Iron Bottom: Didn't mean to imply Shuemann's information was misleading. As a matter of fact if I put myself in his shoes I get the heebie-jeebies just thinking of somebody filing the back of the feet, not keeping the radius, and having the feet crack & separate from the barrel - a barrel I (Shuemann) made! (I've heard this can happen)

I've only hard fitted one barrel, did it about 42 years ago, and am pushing 67 years of age. Still have and shoot this old GI 1911 (my one and only 1911). I'm just saying if I ever hard fit another new barrel (even one of Mr. Shuemann's) and need to either file the feet or VIS to get it to work, I'll file (carefully, keeping the radius like I did previously) the feet first before even thinking of moving the VIS back. This is partly because the VIS in my gun is about 0.005 farther back than the upper specification limit.

I've got a spare barrel (such as it is), but no spare receiver.

The only way the barrel can stop on the frame bed instead of the VIS is if it is stopping on the link.

Any contact with the frame bed should be minimal and occur after contact with the VIS.

Link length will determine proper distance from the slide stop pin to the VIS. If this needs correction, best to remove material from the rear of the barrel's lower lugs, if the VIS is correctly located.

Filing on a VIS to move it back gives me the heebie-jeebies. Too easy to cut it at an angle and leave the lower area sitting too far forward. Not the place that you want the tips of the lug feet to smack.

Lub... I've seen two barrels that hit the bed hard just before or just as they hit the VIS. Neither were stopping on the link, and both pulled through the chamber floor with a spread-legged "U" shaped crack... wider at the back. The lug wasn't separated from the barrel at the rear... but another 100 rounds probably would have done it. Both were mid-production ORM Colts. Rare... but it can happen. Tolerances stacked up in the wrong direction.

Stopping on the bed would put less pulling force on the lugs, no?

Usually when a barrel fails in this manner it is due to lack of the VIS relief.

Interesting that Schuemann notes that failures of this type are not uncommon with 416S steel due to sulfur stringers... the very material he uses for his barrels.

Also interesting that Springer 2 pc barrels exhibit the most common lower lug pull-outs, yet Springer frames commonly lack the VIS relief.

I've seen more than a few IPSC 38 supers barrels shear the lower lugs completely off! Most, but not all of the time, this was attributable to improper linkdown.

I've never seen a forged chrome-moly Kart fail like this, even improperly fitted.

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Stopping on the bed would put less pulling force on the lugs, no

Usually when a barrel fails in this manner it is due to lack of the VIS relief.

Probably... but here's what I found in both cases.

Very small amount of clearance when in bed. Something on the order of .007 inch, IIRC. There was no visible damage to the front corners of the upper lugs, as is often seen with timing issues. The rear of the lower lug was also undamaged, which indicates that there wasn't a problem with the barrel getting caught between slide and VIS. The chambers didn't fail at the rear junction of lower lug and barrel. It was slightly forward of the rear of the lug... about 1/8th inch or so. There was no peening evident on the VIS, nor was there any indication of hard contact at the lower lug feet on the VIS.

There was evidence of hard contact at the frame bed and lower barrel radius in the form of deep burnishing that almost looked like skid marks. Odd...

There was evidence of scuffing on the tops of the upper lugs and hood area, which I figured to be coming from the barrels just narrowly clearing the slide as they linked down.

The VIS in both guns were slightly rearward of mid-spec... but still within tolerance.

The field-test for stopping on the links produced a completely free-swinging slidestop pin on one, and the tinies bit of bind on the other. I could move the slidestop arm with a light flick of a fingernail... so on that one, the barrel was stopping on the VIS, but still had the link and crosspin in light tension... very light, and not enough to stress the lower lug.

Neither link had been stretched... but both were shorter than the standard .278 when measured across pins. Both were about .003 inch short, but again... neither was in hard tension when the barrel was fully down. Flipping the guns upside down and racking the slides produced a slight hitch at the linkdown points tha wasn't apparent with the guns rightside up, or tilted down at 45 degrees. Only when held upside down. The hitch was very slight.

Assessment was that the barrels were hitting the beds at the same time, or possibly slighty ahead of hitting the VIS. A check of the bed height to the frame rails showed both to be slightly higher than mid-spec, though both were within allowable tolerance. With perfectly clean guns, the drop timing probably wasn't an issue. When a little carbon built up on the bed, it likely brought on the stresses that did the barrels in. A quick barrel switch from two of my Colts gave the same indications of a problem there, since all dimensions were virtually identical. The owners wanted to replace the barrels with OEM Colt barrels, and I ordered the parts... along with Wilson #3 links... and replaced the barrels.

To prevent a repeat of the barrel failures, I deepened the beds in both frames to provide .015 inch of drop clearance with the slides. Both guns have been chuggin' along for about 5 years now under fairly heavy use, and the barrels are still good.

Hi Tuner: Did the skid marks you refer to in Post #19, this thread, resemble those in Lazarus's pictures in Post #42 of his thread "Link Fitting - Voice Of Experience Needed"?

NIEMi24s, I had a feeling that wasn't going to sound exactly right, but couldn't think of any way to sugar coat it. Sixty seven. Hope I can say that one day. I deal with a lot of customer modified things and know of what you speak.

The experience you speak of with your Colt's barrel fitting, 42 years of reliable service, is what I would like to accomplish with the one I'm messing with now. I would like to have the frame, slide, link and barrel I am having to deal with be able to go the distance. If this requires a little machine work on any of these parts, so be it. A good trade off for reliability in my opinion. And my opinion is worth exactly what you paid for it.

The only barrel I have seen with the bottom lug torn almost all the way off was a Kart. The tearout was almost complete with the exception of a small bit of steel in front of the lug holding the lug on. Kinda like the lug was sitting on an island. The tear did not extend into the chamber. I concluded that the bottom of the barrel feet were making contact with the VIS due to the gouges in the VIS and the peening of the back of the barrel feet. So perhaps any barrel can be destroyed with improper fitting.

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Hi Tuner: Did the skid marks you refer to in Post #19, this thread, resemble those in Lazarus's pictures in Post #42 of his thread "Link Fitting - Voice Of Experience Needed"?

No. Harder contact than that. Those appear to be normal contact marks.

Use a piece of cold-rolled round stock to polish a like-sized radius in another piece of cold-rolled steel. It had a burnished, melted appearance... almost like metal had been transferred, except none had been.

Hi Iron Bottom: Didn't want you get the goofy idea that I was some sort of whiz with the 1911. I'm just a shade tree gun plumber [and a lucky one too!]. After I got the gun (a cobbled together GI with a Union Switch & Signal receiver, Remington Rand slide and Colt GI barrel), I fitted a 1965 National Match barrel by H&R following the instructions in an article in the December 1963 American Rifleman and some other advise & tips. This work included a slide "squeeze job" and the initial peening down of the receiver rails. The rails have been peened down two more times, and have now been lowered and worn down about 0.008 inch below mid-spec. The receiver's top now looks like the top of an old anvil!

I'm still trying to learn how the 1911 works and how to keep it working. This forum has been a real blessing in that regard, as the vast majority of my smarts about the 1911 have come from you folks. Thanks - to all of you.

Does Anyone have any pictures to show on this very interesting subject? And exactly where the barrel lugs should rest on the pin?

The photos I posted exaggerate the wear marks that appear on the bed. These marks are in reality extremely faint, but have caught the light just right in these photos to look worse than they are. In fact, these marks appear to me to be machining irregularities that have been left by the machine shop, and not by barrel banging. In any case I have shot maybe 150 rounds total in this gun!

A question if you don't mind... would someone point me to the description of linkdown testing involving the slide stop? I gather that there was a post describing that the slide stop would be free to rotate if pressure were applied to the muzzle in linkdown. After careful testing, I see that my original assessment was incorrect. With the gun inverted, there is a slight hitch when pushing the slide back into battery. The hitch happens just at the point when the barrel's upper lugs need to engage into the slide. It is minor, but I feel it now. I was too aggressive before and did not notice. I'm wondering what part of the barrel camming is being tested when the gun is inverted?

I hope Tuner, Lubaloy, and some of the other pros weigh in on this... meantime, go to the Schuemann barrel site and read the Timing Test Kit section - it's the best explanation of what should be happening, what can go wrong, and how to test for it that I've seen, it also includes the clearances he recommends, how to check them (you don't really need the kit), and how to get the clearances.

But keep in mind that his is only one opinion, and some of the pros on this site seem to me to be satisfied with clearances (and methods for getting them) that differ from Schuemann.

I think the Tuner recommended test of cycling the gun upside down is another way to remove any slack in the link as it hits the VIS. Similar to Schuemanns test 2.

So, holding the gun upside down and cycling (without recoil spring) primarily focuses on the slide coming out of battery... that makes sense. Is the slide stop test one of Schuemann's timing tests? It is hard to keep them straight. Pressing the muzzle against a table would force the barrel lugs against the VIS. However, the slide stop would not be free to rotate unless the link were totally unstressed at that point.

Actually, I think it would check both going in and coming out - it removes vertical drop of the barrel due to gravity and allowed by link / pin slack, if any exists. When actually fired, things move fast and inertia will remove any slop, and this is a way to simulate that.

But I'm guessing, Tuner is a true expert and will I hope he'll speak more to this. Also, some of the stickies address the issue.

The free slide stop test is one of the 'false' tests Schuemann mentions at the end of the writeup if I remember right. If everything's perfect, the ss should be in slight compression at full linkdown.

Ref: Your Q, Post #25, about linkdown testing involving the slide stop.

1. The test method involves removing the recoil spring, plug, and guide rod, then reassembling the gun but with the slide stop lever hanging straight down over the trigger guard. Move the slide aft enough to unlock the barrel from the slide and then simultaneously push the barrel fully rearward (push muzzle against a table) and the rear of barrel fully down (push with finger through ejection port). Then, while keeping these two pressures on the barrel, see if the slide stop's lever is free to swing back & forth by flicking it with a finger and...

A. If it does swing freely it means there is no pressure exerted on the slide stop pin by the link. This means the link is not in compression and the barrel's downward movement has been stopped by the barrel bed in the receiver (assuming it's not been stopped by interference with the slide's bore or the barrel feet bottoms contacting the receiver recess). Some people claim the barrel's downward movement should be stopped by bed contact. If the slide stop lever is completely free to swing under the test conditions the gun passes their test.

B. If it does not swing freely and is quite hard to move it means there is pressure exerted on the slide stop pin by the link. This means the link is in compression. The barrel's downward movement has been stopped by the aft surface of the barrel's feet sliding down along the VIS until the link is squeezed between the slide stop pin and the barrel link pin/barrel. All this without the barrel contacting the receiver bed. Some other people claim the barrel's downward motion should be stopped by VIS/link in compression - with no bed contact. If the slide stop lever is not free to swing under the test conditions the gun passes the test of these people.

C. The third possible outcome of this test is probably a fairly rare one. It's actually right in between A and B. The slide stop lever won't freely swing back & forth when flicked with a finger, but it'll move a little bit. If this is the test outcome, it means the barrel's downward movement has been stopped by both the VIS/link in (a little bit of) compression and the barrel bed. For those claiming the job of halting the barrel's downward motion should be shared by the VIS/link and the bed, if the slide stop lever's not too loose but not too tight, the gun passes their test.

Bear in mind all this concerns testing for what halts the barrel's DOWNWARD movement. Its rearward movement should only be halted by contact with the VIS - and NOT the link in tension in conjunction with the bed.

Got no idea (now) what's best - A or B. At present, my old target plugger meets the criteria in C! All I'm pretty certain of is that (based on Ordnance Dept blueprint specs), most USGI 1911A1's would have loose slide stops at linkdown and fall into para. A, above (See Post #1, this Thread).

To check for short link/VIS too far rearward/Lower lug too far forward...

Push the barrel as far rearward as it will go against the edge of a table. The slidestop arm should swing free. If it doesn't, the barrel's rearward movement is being stopped by the link in extension. Bad juju. Baaaaaaaad JUJU!

With the slide fully rearward, rearward pressure off the barrel... push it down firmly. If the slidestop arm swings free, the barrel's drop is stopped by the frame bed. If it gets into a slight bind, it's being stopped by the link in compression. Check to see how FAR off the bed the barrel is stopping. More than a thousandth or two... or more than a slight bind of the slidestop pin is bad juju, but easily corrected.

Stopping the drop on the link in compression is rarely seen anymore, except in a very carefully fitted pistol... and few of those do. Most stop on the bed. As long as they don't hit the bed first or at the same time... Heap gooooood medicine. The barrel should stop against the VIS near the radius at the top of the lug and drop the last couple of thousandths to bed. The farther down on the lug the impact is focused, the more likely you are to have a lower lug failure. This is the reason for the bowtie cut. It's not to correct a timing problem wrought by the VIS too far forward. It's to get the impact stress off the lower lug feet, and is unnecessary if the VIS is within spec... and is generally done as more of a preventive measure than out of necessity. In any event, the cut shouldn't be more than about .003 inch deep... IMNSHO.

At the point of impact with the VIS, sufficient clearance should exist between the top of the barrel and the slide at the proscribed .250 inch of slide travel. It can occur a little earlier... but should occur no later.

Schuemann and 1911Tuner are in agreement on the main of Tuner's post, and for me that just flat ends the argument.

But 2 more of my endless questions, please... what is 'sufficient clearance' above? Schuemann wants .015 while the link is still in tension (just as VIS impact occurs, and before any vertical drop occurs). That .015 is huge. I cannot get it with Caspian frames without moving the VIS to the rear, or the back of the lower lugs forward.

Changing links doesn't help... on my gun a #2 is too short (gun won't go into battery) and #3 is too long (slide 'snaps' into battery as barrel passes vertical). Used a #3 with link pin side relieved .002, per an earlier Tuner post.

Q2... Why is the .250 max important? I understand why a minimum amount of slide travel is needed, but I can't see yet why it matters if the slide moves more than .250 before full linkdown occurs?

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Q2... Why is the .250 max important? I understand why a minimum amount of slide travel is needed, but I can't see yet why it matters if the slide moves more than .250 before full linkdown occurs?

Time. Nothing moves instantaneously. It takes time to accelerate an object. Linkdown begins at about .100 inch ofslide travel. That means that it's only got .150 inch to drop a 64th inch.

My 1911A1 is set up so the barrel's rearward motion is stopped by VIS (bowtie) contact and its downward motion is stopped by contact with the forward part of the bed. The slide stop is under light pressure from the link. In Post #30, the instructions say this is OK as long as VIS contact is made before bed contact is made.

Q: How can I tell whether the barrel hits the VIS first (then the bed) or the bed first (then the VIS)?

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Q: How can I tell whether the barrel hits the VIS first (then the bed) or the bed first (then the VIS)?

Place a strip of carbon paper on the bed and onto the VIS. Recoil system left out... Start with the slide in battery. Whack the end of the muzzle with a plastic mallet and look to see where the contact is by observing the carbon marks. Blued surfaces may require removal of the bluing to clearly mark the areas. Touch-up with cold blue afterward if you want.

A quick-test to determine if the barrel drop is stopping on the link in compression is to pull the slide back to .250 inch and press down on the barrel firmly to see if it drops a little further.

Thanks for the added info. I went back to Schuemanns site and see that the swinging slide stop info is under the heading "Invalid Fad". One random question is what does the test spring look like, so I can make one up?

Another random question: Schuemann says to contact KKM Precision barrels here:

http://www.kkmprecision.com/index.html

for the timing test kits, but nothing on their site refers to the kit.

In addition, KKM barrels are all made of 416 stainless. After reading Schuemanns rant about what a poor choice 416 is for gun barrels, I'm amazed he wants to send people to a stainless barrel maker.

In any case, using the "invalid fad" method, with rearward pressure on my unlocked barrel, the s.s. swings freely. With no rearward force, pressing down on the hood of the unlocked barrel also results in a free s.s. Hmmmm. After all the precise measuring, too!!! The difference between a loose stop and a tight stop is a matter of a few tenths. Usually it is not real clear how or when to remove a few tenths, as this is usually done by lapping.

Random observation. My Kart NM barrel came with added meat in the area between the barrel lower lugs and the rear of the barrel. You can easily see the machining marks that cut metal at about the 4 o'clock and 8 o'clock positions. That left a few thousandths extra right where the barrel would "sit down" on the frame bridge. With all the foregoing barrel fitting instructions whirling in my head, I judiciously removed a few thou in that area, to insure some clearance and to remove the high spots left over from milling. Also, I did smooth the vertical lug surface on the barrel because there was a nice circular milling mark standing up right where the "bowtie" would smack it. Things just aren't as easy as they should be!

But, I'll be the first to report it if my lower lugs rip away from the chamber! I have not done the carbon paper test yet, but this is next on my list. Right now, I'm trying to determine what the slight hitch I feel when cycling an inverted gun means. A very slight hitch just before the point where the barrel upper lugs move into the slide lugs.

More coffee please. My head is hurting with all the timing instructions, slidestop warnings and pictures of ripped up 1911 barrels.

One more thing that has been referred to is the "link in compression". Perhaps this term needs to be defined a bit more. Using one of JK's drawings of the gun in linkdown, you can see the link sitting at about 45 degrees to the axis of the gun. Draw a little triangle using tracing paper. The points of the triangle will be the slide stop pin (point A), the barrel link pin (point B) and the point of contact between the barrel lugs and the VIS (point C).

There is an arrangement that would put the link into compression, another that would put it in tension, and I suppose a very delicate arrangement that would result in neither tension nor compression. Mechanical engineers please step in here. I am too confused right now to go further, but the actual difference between the 3 possible outcomes is preciously small, I can tell you that!

A downward force on the link pin B would put the link, A-B and the leg B-C in compression, leaving the bottom leg which is the frame, A-C in tension.

An upward force on the link pin B would put the link and leg B-C into tension, with the lower leg (the frame) A-C in compression. Note that there is no actual movement required (theoretically) to achieve either condition.

So how do we get a link that is not being stressed at all? Time to say goodnight, Chet. Goodnight Chet; Goodnight David. (lifted unscrupulously from the Huntley-Brinkley Report).

Sorry Laz... I couldn't see your post, but it was cut and pasted for me because it was... what's the word... Classic! So... I'll respond one more time for the readers who are trying to learn something instead of trying to find something to nit-pick me to death over.

Nowhere did I say that the free-swinging slidestop pin method was a timing test. Read it through again. We'll wait...

Nowhere. It's a quick check to see if the barrel is being stopped by the link, Either because the VIS is located too far aft... or because the barrel lug is located too far forward... or because the link is too short... and that's all it is.

Since you're fond of quoting from text... I'll follow suit and paste a direct quote from Schuemann's excellent tutorial that addresses that very subject.

To wit:

"Assuming you have read and understood the 1911 Test Kit section of this web site you will be able to figure out that the above test, in fact, does check if the frame impact surface is too far aft."

See where it says: "Assuming that you have read and understood"

I suggest that you go back and read it again in order to enhance your understanding.

Question, sir. Pistol is in battery and link is standing vertical. Wouldn't any rearward movement of the slide and barrel result in the barrel dropping immediately? Assuming no play in the linkage and slipe stop pin and frame, of course. In other words, is it necessary for the link to break over vertical toward the muzzle when in battery to give the slide and barrel the necessary reward travel before starting to unlock? BTW, Tuner, I was coming down to see you but could not PM you. Kept getting some message about not being able to locate you. I got a warning for pinging you. I hope this is ok with the Mods.

I think I have found a problem with a sloppy link and slide stop pin fit. This may clear up some link down problems I am having.

Lazarus, if I remember correctly, you posted re firing your pistol with the slide .100 reward of the frame. I am thinking that this pistol was very close to firing out of battery unless that slide or frame was really out of spec. I am surprised it fired at all. Another good reason for an EGW firing pin stop with the small radius. Keeps the hammer off the firing pin a little longer. Keeping in mind that the slide needs around .100 of reward travel before starting to unlock, do you think you may have damaged the upper barrel and slide lugs in any way?

Don't know what Mr. Schuemann's test spring looks like, but he describes its function as: when inserted through the dust cover hole, the end against the front of the barrel's feet lifts the aft end of the barrel upward when the other end is pushed downward. This other end is pushed downward by the underside of the table when the gun's muzzle is raised. The bottom of the dust cover acts as the fulcrum point between the two ends of the spring.

I did Mr. Schuemann's test without his test spring by using an aluminum shotgun cleaning rod which had a moveable depth stop on the handle section. The depth stop was set for about 4 1/2 inches (so the end of the rod would only get to the middle of the chamber) and the rod inserted into the muzzle of the 1911. A similar gizmo could be made from a piece of 3/8 or 7/16 inch diameter dowel with a depth stop of some sort. Just make sure whatever you poke down the barrel won't harm its lands.

Just put it down the barrel. When the other end is under the table and the gun muzzle raised, the dowel "teeters" at the muzzle and forces the chamber end of the barrel upward to remove the slack from the link - just like Mr. Schuemann calls for. It worked for this shade tree gun plumber.

I'm guessing Mr. Schuemann devised his test spring as a way to avoid somebody putting anything inside one of his barrels and causing bore damage. Very smart thinking on his part.

Neimi24s described exactly why the timing test kit isn't required.

I hold the frame in a vise, brass rod down the barrel til mid-chamber, hold the rod so my thumb can press the barrel to the rear and then lifting up the chamber while the barrel is pressed rearward. That way you have removed the vertical slop and have a free hand to measure the clearance - I use a dial indicator, you can measure the clearance by releasing the rearward pressure which allows the barrel to move up to slide contact.

I'd still like other opinions of what sufficient barrel / slide clearance is at that point?? Or is Schuemann's .015 it?

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Time. Nothing moves instantaneously. It takes time to accelerate an object. Linkdown begins at about .100 inch ofslide travel. That means that it's only got .150 inch to drop a 64th inch.

I'll run the risk of nitpicking here, which I promise is not my intent

If the bullet clears the barrel at .100 or so, and linkdown begins, acceleration ends at that point or very near it - bullet is gone and forces now cease. There may also be a very short jet effect, seems to be some disagreement on this. Anyhow, after the first .100 or so it's all over and now just a matter stopping the slide at the end of it's travel.

So I'm still having trouble understanding why the .250 limit is critical. Maybe I'm dense (probably), I've read all of the related posts and links - if the answer is there I missed it. As a practical matter, with a #3 link and VIS at the correct location, linkdown will end at around .250 - trigonometry says it has to. But what about a #5 link, if one were ever used? Seems like full linkdown should take longer.

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Question, sir. Pistol is in battery and link is standing vertical. Wouldn't any rearward movement of the slide and barrel result in the barrel dropping immediately? Assuming no play in the linkage and slipe stop pin and frame, of course. In other words, is it necessary for the link to break over vertical toward the muzzle when in battery to give the slide and barrel the necessary reward travel before starting to unlock?

Ya answered your own question, mah fren. Yes. Assuming that the lower lug hasn't been altered to delay linkdown and drop and that the barrel isn't riding the link... it will start almost immediately. The link swings slightly past BDC... toward the chamber end... not the muzzle.

I wondered why ya didn't show. Can't figure why my PM told ya to go away. Odd.

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Neimi24s described exactly why the timing test kit isn't required.

I hold the frame in a vise, brass rod down the barrel til mid-chamber, hold the rod so my thumb can press the barrel to the rear and then lifting up the chamber while the barrel is pressed rearward. That way you have removed the vertical slop and have a free hand to measure the clearance - I use a dial indicator, you can measure the clearance by releasing the rearward pressure which allows the barrel to move up to slide contact.

I'd still like other opinions of what sufficient barrel / slide clearance is at that point?? Or is Schuemann's .015 it?

I'll run the risk of nitpicking here, which I promise is not my intent

If the bullet clears the barrel at .100 or so, and linkdown begins, acceleration ends at that point or very near it - bullet is gone and forces now cease. There may also be a very short jet effect, seems to be some disagreement on this. Anyhow, after the first .100 or so it's all over and now just a matter stopping the slide at the end of it's travel.

So I'm still having trouble understanding why the .250 limit is critical. Maybe I'm dense (probably), I've read all of the related posts and links - if the answer is there I missed it. As a practical matter, with a #3 link and VIS at the correct location, linkdown will end at around .250 - trigonometry says it has to. But what about a #5 link, if one were ever used? Seems like full linkdown should take longer.

It ain't nitpickin' if you're tryin' to sort out a misunderstandin'.

Actually, slide acceleration after the impulse... while the bullet is traversing the barrel... is pretty negligible. While dwell time in the barrel can make or break the slide's cycle in some of the chopped variants firing lightweight, speedy bullets... the slide gets almost all it needs during the first inch or so of bullet acceleration. Any "push" afforded by the bullet after that point is unnecessary for full slide cycle. I've reamed the rifling out of the barrel all the way to the chamber shoulder, for a finished bore diameter of .495 inch...fired a round of standard hardball... and the slide cycle showed very little change. The empty ejected and fell within a foot of where it would have with an unaltered barrel... and the bullet penetrated out of sight into a hardwood tree. I couldn't detect any difference in felt recoil, other than the fact that the gun didn't torque to the right.

The .250-inch thing can vary a little... and can go a bit farther in some guns, depending on other variables in the linkdown/drop function. The .250 inch directive is a lot like a maximum recommended powder charge listed in a reloading manual. What they're saying is: "Some guns will tolerate more pressure, but this is the cutoff line that'll keep you out of trouble with any given gun.

On the #5 link:

Long links are used when a given gun's vertical dimensions place the slide and barrel farther away from the slidestop pin hole, and are correctly used after a full hard-fit has been done to the lower lug/slidestop pin to effect a solid vertical barrel engagement... and the standard link is too short to let the slidestop pin slip through the link's hole and clear the forward radius of the lug for linkdown and barrel drop. In other words... The longer than standard link compensates for when the frame and slide are taller than mid- spec.

Many people who don't understand what the link does and why... will install a long link in order to compensate for an overcut lower lug to tighten vertical engagement. If the frame and slide are mid-spec, and the lower lug is out of spec... the linkdown and drop timing is compromised, and trouble looms. If the loose vertical engagement is because the slide sits higher than mid-spec on the frame, placing the barrel lug farther away from the slidestop pin, it won't cause timing problems... IF... the link selected is the right link..and that's where it gets hinky. If a link is selected purely on the fact that it tightens vertical engagement, without knowing the vertical dimensions of the frame and slide, it becomes a cra.... er... a roll of the dice. ya might get lucky, and ya might not.

If the link is so long that it stops the barrel in compression too far off the frame bed to let the lugs completely disengage, you have much the same problem as with the VIS located too far forward, with the attendant damage to the upper and lower lugs. If the link is so long that it delays linkdown timing beyond the allowable parameters... same thing... though the damage is generally not as immediately apparent. One lets you know right away that you've got a problem because the barrel stops the slide in its tracks. The other lets the slide skin by, but the corners of the upper lugs become radiused and flanged.

Going in the other direction, and installing a short link to get the barrel off of it... riding the link... and you advance the beginning of the linkdown event.

The link works to disengage the barrel earlier in the cycle, and sometimes it tries to start the barrel before the bullet exits. Pressure is still on the lugs, and damage is also possible here because it's trying to effect a vertical movement at 90 degrees to a hard horizontal engagement.

So... Dinking around with links is dicey unless you've taken the critical measurements and determined that the link's on-center length is correct for that particular gun.

The .015 inch minumum drop is another one of those standards that'll keep you out of trouble in any given gun. If the gun is precisely fitted, and the drop timing is just so... you can get away with less... maybe as little as .005- .007 inch. The .015 parameter just provides a little more wiggle room if your calculations are off.

Outstanding post John! Everyone hears that 'riding the link' is a no-no but that's the first comprehensive explanation I've seen of the mechanics of why.

Right, Tuner. The chamber it is. I was looking at the top of the link. In Shuemann's barrel fitting test he makes the comment "with the link vertical and in battery" or something to that effect. Made me wonder if he was talking about the link being perpindicular to the frame rails or if I had missed something. In my case the link does stop over vertical toward the chamber.

Anyhoo, I'm going to order some links and a slide stop and hopefully cure this clearence caper. I have clearence until Shuemann's test is performed (levering the rear of the barrel upwards) and if a new link and slide stop prevents the barrel from contacting the slide in any way, shape, form or fashion, .005-.007 would be good, I'm gonna call it good to go.

Canuck... I dunno if you could call it comprehensive, but it was the best I could do on short notice. That link... so simple in its design... can be so complex in its function.

Iron Bottom... The clearance can be adjusted a little, and .015 inch isn't hard to get. it's not so much the actual clearance as it is the timing... when the clearance comes. Speed of the drop after disengagement is another factor.

You can have a full 32nd inch of in-bed clearance, but if the drop starts late or is too slow, it about might as well not drop at all. Bring it back down here and let me take a look at it. Sometimes it's a matter of a little adjustment here and a little there... the striking of a balance... that sets things right.

I'm pretty good to go any day except Thursday, and will advise if anything comes up in the meantime.

However, the middle condition (where the barrel's on the bed and the VIS) can exist over a seemingly wide range of link lengths - about 0.010 inch. This is due to the tolerances and clearances between the parts connecting the link to the barrel and to the receiver.

To help visualize this stuff I playied a "mind game" pretending to be a link. A young, way below spec, but still growing link. Started out just short enough to prevent the feet from contacting the VIS at linkdown. Baaaad boy, as Tuner said, because I was in tension and doomed to fail at some point. Continued growth allowed the feet to get closer and closer to the VIS until light contact was finally made, but I was still under lots of tension. More growth finally eased the tension to zero, at which time I became loose between the two pins going thru me. While I grew about another 0.010 inch, I remained a loose little link, and the barrel remained snuggled up against the VIS and the receiver bed. But then all the clearances between all the parts around me got reversed and taken up in the other direction. I finally started to feel a little bit compressed, and was no longer a loose link. As this feeling (compression) grew, I began to lift and slide the feet upward along the VIS until the barrel lost all contact with the bed. I was now under full compression, and a fully-grown link. The End.

BTW, the determination of about 0.010 inch of total "slop" between all these parts is based mostly on Ordnance Dept. blueprint data, but partly on measurements of a new, unused Colt standard ".278" link and barrel link pin. Had no specs for these. If somebody'd be kind enough to share these specs including tolerances with me I'll re-do the math and edit in a new "slop" figure, if necessary.

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Had no specs for these. If somebody'd be kind enough to share these specs including tolerances with me I'll re-do the math and edit in a new "slop" figure, if necessary.

Whew! At this point... to save mucho time and bandwidth... I'd suggest a copy of

Kuhnhausen, Volume 2 and a full pot of coffee. You'll be a while sortin' it all out.

Link specs are: c-c .278 + or - .001
barrel link pin .156 R-.005
slide stop pin .184 R-.005

slide stop .2005 Dia-.0020

frame .201 DIA+.002

These figures are for the 1911A1 and are taken from the Eric A. Nicolaus publication.

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Link specs are: c-c .278 + or - .001
 barrel link pin .156 R-.005
 slide stop pin .184 R-.005
 
 slide stop .2005 Dia-.0020
 
 frame .201 DIA+.002
 
 These figures are for the 1911A1 and are taken from the Eric A. Nicolaus 
publication. 

You sure those numbers are accurate?

The gun I've just finished is closly fitted... #2 is too short (won't close), #3 is too long ('snaps' as link passes vertical into battery). So it's a #3 relieved at the link end, I think this also helps the gun not to ride the link - it doesn't.

But only .006 on the Schuemann torture test and I see no way to increase it. I've blued the barrel lugs, absolutely no sign of lug polishing / rounding, and the gun is very accurate, smooth, reliable. Linkdown begins at .110, full unlock is .249 best I can measure it.

But that .006 worries me a bit, I'll just have to watch for any link or pin wear.

gbw... Is the barrel sitting full down onto the bed or is it being held off by the link?

Thanks for the speedy reply, but . . . Suspect the one given for the hole for the barrel link pin should, maybe, be 0.1560D -0.0005 just because the minimum for the one given (0.151) is 0.003 less than the minimum spec for the link pin hole in the barrel. Also, the spec for the link's hole for the slide stop pin (0.184 -0.005) is way less than the slide stop pin itself.

FWIW, my measurements of an unused Colt link showed 0.1567 and 0.2050 for the hole diameters using taper pins to transfer the measurements to a good 0.0001" resolution micrometer, repeated 8 times and averaged for each hole. But, this particular link could be out-of-spec for all I know.

Anyway, if this is what's in the Nicolaus book for the link I'd be suspicious of any of the other dimensions and tolerances. Regards.

The first three figures are for the link only, not the pins themselves. The barrel link pin is speced at .1555-0010. The only figure I suspect is the drilling in the link (bottom one in the link at .184 R-.005) since it will have to be reamed for the slide lock pin. Maybe the link was reamed to fit the slide lock pin? The other figures look OK. The print notes that the link was redrawn and revised on 27NOV62 from an "A" size link. The author says he got these prints through the Freedom of Information Act from the Federal Government. But the only thing standard about standard 1911 parts that I've noticed is that none of them are standard.

GBW, Dawson Precision has links in .0025 increments.

Hi Iron Bottom: Thanx for the specs for the link and the pin in Posts 48 & 53. I'll use them and my measurement for the link's large hole to re-do all the math and post the results. Gimme a day - my head hurts bad!

Keep in mind this has nothing to do with what size link is needed to allow the gun to go into battery or to be properly timed. It's merely about determining the maximum amount a link's length can be changed and still allow the link and slide stop to be loose at linkdown. Regardless of whether or not they should be loose at linkdown.

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Keep in mind this has nothing to do with what size link is needed to allow the gun to go into battery or to be properly timed.

Before you start... Understand that the link doesn't have anything to do with the gun going to battery, with the possible exception of the condition of the barrel riding the link... and that's essentially a misfunction anyway. The barrel goes to battery because the slide pushes it into battery. The link's *only* function is to disengage the barrel from the slide during the recoil cycle.

Not pickin' on ya... just tryin' to help eliminate one point of confusion so you can concentrate on the task at hand.

No problem, NIEMI. Does Santa leave headache medications for forum members? I think I understand what you are doing. And this will be a great help to me and others to be able to have some idea of what they're getting into. I'm starting to think that if a .040 lug engagement is possible with a standard link (.278) go for it and save yourself a lot of headaches. Perhaps a little more lug engagement if the barrel feet aren't landing correctly on the VIS and barrel bed.

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gbw... Is the barrel sitting full down onto the bed or is it being held off by the link?

The barrel does not touch the bed, it's held slightly off by the link - I haven't measured the distance off, but it does not touch. I'll try to measure it tonight.

One other note, the lower lugs thinnest section measured horizontally is .091.

I'm not sure at what point they are too thin, and for sure I don't understand the stress dynamics there, i.e. a round relief in the lugs hitting a round ss pin, especially with the barrel so closely fitted - essentially no vertical clearances in battery. Even still the slide still very slightly overhangs the rear of the frame. No sigh of deformation at 250 rounds, standard Wolff springs.

When I built my first pair of guns a couple of years ago, I though I knew what I was doing. I didn't know s, er, anything. It's pure dumb luck they work as well as they do.

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The barrel does not touch the bed, it's held slightly off by the link - I haven't measured the distance off, but it does not touch.

If the barrel's linkdown and drop is timed right, you can gain a little more clearance by altering the link at the top of the slidestop crosspin hole. It's not imperative that the barrel not hit the bed, as long as it doesn't hit it too hard or ahead of the VIS.

Sorry, I wasn't clear, I was talking about the clearance with all vertical slack removed - Schuemann's test with the barrel pressed fully rearward and the chamber end lifted upward. So relieving the link wouldn't help, or am I mistaken?

One other note, the lower lugs thinnest section measured horizontally is .091.

I'm not sure at what point they are too thin, and for sure I don't understand the stress dynamics there, i.e. a round relief in the lugs hitting a round ss pin, especially with the barrel so closely fitted - essentially no vertical clearances in battery.

Even still the slide still very slightly overhangs the rear of the frame. No sigh of deformation at 250 rounds, standard Wolff springs.

Head quit hurting, so using the Ordnance Dept specs, Iron Bottom's specs and an assumed link large hole diameter of 0.205 inch the calculations were all re-done. A close-to (because the 0.205 used is from a measurement, not a spec) mid spec GI 1911 has 0.009 inch of slop in its link system. This is with no interfering contact between the feet and the slide stop pin. [I'd said 0.010 inch previously]

Put another way, there's 0.009 inch (measured along a line thru the link hole centers) of movement between the barrel and receiver as the link goes from being in tension, then loose, to being in compression (or compression, loose, tension).

It also means that (by my calculations) a close-to mid spec GI 1911 has a link that's a mere 0.0015 inch longer than necessary to avoid being in tension at linkdown! JMB was truly a genius of the first order!!

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Sorry, I wasn't clear, I was talking about the clearance with all vertical slack removed - Schuemann's test with the barrel pressed fully rearward and the chamber end lifted upward. So relieving the link wouldn't help, or am I mistaken?

From the sounds of it, you could probably do with a .005 inch shorter link. If you're presently using a Wilson #3, try a #2 and check for slidestop pin binding with the barrel full down and back.

Yeah, I tried that. A #2 is too short and does not allow the gun into battery. The barrel in battery is a hard fit, so no vertical play exists. Me thinks I'm stuck.

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Yeah, I tried that. A #2 is too short and does not allow the gun into battery. The barrel in battery is a hard fit, so no vertical play exists. Me thinks I'm stuck.

Will the barrel fall to bed with sufficient clearance at the top if the link is removed?

EGW offers an oversized slide pin as you probably already know O/S .2000+/- 005.

Would this pin help when using #3 link depending on frame hole size?

Hi GBW: In Post #65, the EGW slide stop is referred to as "oversize" with a pin diameter of ".2000+/-005.". However, a zero was omitted from the tolerance portion, cuz the EGW website shows its diameter as ".2000+/-.0005". BIG difference. Anyhow, before jumping off the deep end and ordering one of these from EGW suggest you mike your slide stop pin to see how much would be gained. Keep in mind the Ordnance Dept. spec for the slide stop pin is o.2005 -.002 inch.

While the EGW pin might be "oversize" in the sense that it's bigger than yours, its upper spec limit is 0.2005 inch. This is exactly the same as the upper Ordnance Dept. spec limit, so in that sense its not really "oversized". However, a mid spec EGW pin would be 0.2000 and a mid spec GI pin would be 0.1995, so in the mid spec sense, it would be considered oversize by half a thou. Plus, the EGW tolerance range is half the GI's range. I'm sure George @ EGW's not trying to mislead anybody here, but is just using the terminology all the other vendors use.

"Oversized" as commonly used just means "bigger than usual", not "bigger than it's supposed to be".

SS pin dia is .200 exactly - this one's a Brown hardcore. I believe you y'all are correct that a bigger stop would help slightly, to the extent it removes play between the SS pin and the frame hole, by holding the centerline of rotation further forward, thus increasing the angle of rotation before the lug hits the VIS.

But the increase would be very small, something like .7 x the clearance reduction between the SS pin and the frame hole, and it would require re- cutting the lower lug. It's a hard fit barrel with no clearance in battery.

As for linking, the gun is fitted closely enough that exactly one link length will work, between #2 and #3, with #3 being closer. So the choice is extend a #2 or shorten a #3.

Ideally, extending a #2 for .0025 would be better the better choice, that way there is slightly less vertical slack at VIS impact - in battery the barrel link would have no slack. I've tried both, and since #3 is closer to right, shortening a #3 decreases the clearance by only .001. On the Schuemann test the extended #2 shows .007, and the shortened #3 gives .006+. Not much difference, and he calls for .015.

Clearance are fine without the slack removed, no problem. Free barrel drop off the frame is .022.

Back on the frame, barrel to the bed unlinked is .018 if I remember right, and linked against the VIS without removing vertical slack (i.e. pressing down on the chamber end insteading of lifting up there) it's on the order of .012.

Maybe at this point it falls into Tuner's "if it ain't broke, don't break it". The gun times perfectly, runs good, now at 400 rds no sign whatever of lug polishing, and no failures of any kind. Lyman 452460 thru hardball. Groups at 1" - 1.5", best I can do with my old eyes.

I was just hoping to get closer to the magic Schuemann .015 linked, against the VIS with vertical clearance pulled out. Only way I can see to get a significant gain is to move the VIS rearward, which I ain't anxious to do.

But as someone else said, you guys are SMART, and if I've missed something y'all will see it.

Could someone please define the term "link in compression" as I'm not sure what it means.

gbw... If you've got those clearances, I'd say you're good to go. If you want to find just the right link... can't remember what the brand name is... but Brownells markets a set in .003 inch increments. (Bob Marvel?) They're listed as + and - using, I suppose, .278 as ground zero.

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Could someone please define the term "link in compression" as I'm not sure what it means.

Hi Ben: What we're talking about is simple... but not. When the gun is fired, slide and barrel move rearward. Barrel unlocks from the slide by being pulled down and away via the link - the link is in tension at this point.

Somewhere later the barrel stops its rearward movement - either by the lower standing lug rear surface hitting the VIS (vertical impact surface) of the frame, which is good... or by the the barrel coming to rest on the frame bed with the link still under tension, which is not good - sooner or later in that case something will break. And link in compression never occurs.

Anyhow. If barrel's rearward travel is stopped by the VIS, the barrel will still move down and downward movement may be stopped by the barrel hitting the bed. This doesn't seem to really hurt anything. There may be some link compression.

The other, most desirable way to stop the downward movement is, if there is still room between the barrel and the bed, for it to be stopped by the link as the barrel's downward movement presses it back toward the slidestop - link in compression.

HTH - there are two excellent sources that discuss all of this further - 1911Tuner's posts on the topic, and the Schuemann Barrel website under the Timing Test Kit section.

This thread has been dynamite. I'm in a little late, but I'd like to throw out some rough numbers regarding the barrel-frame collision at linkdown.

Say the slide/barrel combo has about 30 times the mass of the bullet. Conservation of momentum will require the initial rearward slide velocity to be about one thirtieth of the bullet velocity (here we are assuming an instantaneous impulse).

So this would lead us to an initial slide velocity of about 27 feet/sec.

At linkdown, just before the collision, we would not expect much of this velocity to have been lost to the spring and to friction (and to the more complex force required to accelerate the barrel downwards). Say the remaining slide velocity is 22 feet/sec.

Since the barrel and slide have just separated, this means the barrel also has a rearward velocity of 22 feet/sec. And if the link is at about 45 deg from vertical at this point, the rearward and downward components of velocity must be equal, so the barrel must also have a downwards v of 22 feet/sec.

Now if the first contact is between the lower lugs and the VIS, the rearward v will be killed (perhaps bounce will actually result in some forward v), but the downward component of v will not be changed much.

So we are talking about a barrel/frame bed collision of perhaps 22 feet/sec (approx. 15mph)! This would be the same as dropping the barrel on to the frame bed from a height of about 7 feet, every shot. Food for thought.

By the way, Tuner, glad to hear about your experiment with the .495 overbored barrel. We need more experiments and less speculation about that .1 sec. cycle we all love.

Your points on the downward/vertical acceleration are valid... but lemme throw another theory into the equation that is demonstrable with a simple experiment.

Attach a baseball to a 10-foot cord, and lash the cord to a tree. Throw the ball in a straight line, and when it reaches the end of its tether, it doesn't just drop to the ground... it accelerates.

So... When the link rotates into position and begins to draw the barrel away from vertical engagement with the slide... would its own rearward momentum cause it to drop even faster than its rearward velocity? I believe it does... and a simple ball on a rope will show that it does.

The demonstration with the overbored barrel was a slam-dunk. I knew what would happen because I'd already had an experience with it during a reckless and misspent youth. When I was 12, me an' this other fool mowed a guy's lawn for a month in exchange for an old Topper 12-gauge shotgun. Not understanding the illegality, we proceeded to turn it into a pistol... actually, a single- shot/snub-nosed 12 gauge shotgun. (It seemed like a good idea at the time.) The first shot nearly dislocated my wrist and elbow... and although I didn't realize it, we proved that projectile velocity has very little to do with free recoil. The scar on my forehead is still visible. I won the bet on the overbored barrel... and then I beat it flat with a sledge hammer.

I'm not quite sure about the geometry of your ball, string, and tree. But force which pulls in the direction of motion speeds up the motion, force which pulls opposite to the motion slows down the motion. And force at right angles to the direction of motion just causes a change in the direction of motion, and does not speed it up or slow it down.

Because of the bearings at each end, the link can only exert force on the barrel at a right angle to the barrel's motion (here there is a small complication because the barrel is pivoting at the bushing, and not keeping the same orientation in space as it moves. I don't think this changes the result significantly.)Thus the link cannot speed or slow the barrel, just change the direction of motion (neglecting all of the usual tiny effects).

The slide can (and does) speed up the barrel rearward, and the link changes some of this to a downwards component. But after the decoupling of slide and barrel, the link can't speed up the barrel.

Stephen Hawking was told that each equation he put into his book "A Brief History of Time" would cut his readership by 50% I'll take the risk here, with an equation in words (so as not to be dependent on browsers):

rate of change of kinetic energy equals force "dot" velocity divided by mass

"dot" is a vector operation that gives an answer of zero if the vectors are perpendicular.

I'll have to defer, since you're apparently more astute with physics equations than I am. Maybe the downward acceleration just seems to be faster because it's a shorter distance, but the redirected momentum of the barrel is definitely providing more to the barrel drop than gravity... although that can't be discounted either. (Everything means something)

You've raised another question, though. (Ain't that the way it always is?)

Wondering how much the barrel drop to bed is affected by rebound in the ones that put the barrel firmly to bed. It would have to have some effect, though probably negligible in a correctly timed gun, due to the short distance involved... but in an example that's right on the peg, it may be enough to bounce the barrel back into the slide's path.

Surely pistolsmiths are a great market segment for headache remedies (especially the really good smiths). Getting a deep understanding of even a simple machine is much more difficult than people think.

Academic engineering knowledge can lead you astray, if you try to force a complex situation into a simple model. Practical experience can lead you astray, if you jump to non-physical conclusions about what is happening.

In almost every field, the masters are much more cautious in their conclusions about the difficult topics, than the apprentices and journeymen are. Beginners jump at easy answers.

By the way, I edited the numbers in my first post, as a result on taking my own advice and actually measuring the mass of a slide I was working from very imperfect memory.

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Academic engineering knowledge can lead you astray, if you try to force a complex situation into a simple model. Practical experience can lead you astray, if you jump to non-physical conclusions about what is happening.

Yep. One of my favorite expressions for describing the 1911 pistol is "Simple Complexity." Fully 98% of my work centers around resolving functional issues rather than in building/creating masterpieces. Most of my "building" is actually in the rebuilding and refitting of old or worn pistols... and returning them to functional reliability. During the course of nearly 43 years doing that, I've long since discovered that most functional problems are simple in nature, and nearly always just as simple to correct.

After 2 weeks of digesting the sage info in this thread and connecting it with Schuemann's timing test instructions (barrel fully rearward and AFT END UP) the little light finally came on in my head.

In Post #1 I said a mid-spec GI 1911 would have its [barrel's] downward motion halted by the bed. This remains true. Tuner said that's OK as long as first contact is made with the VIS (which halts rearward motion). The key seems to be that the link is in tension when the barrel (its feet or chamber bottom) makes first contact with the frame - like Schuemann says. Ahhhhh, honorable masters, grasshopper finally get big picture.

How far is the barrel bottom above the receiver bed when VIS contact is first made in a mid-spec 1911? After finally getting some reliable specs for the link, it worked out mathematically to be 0.010 inch at mid-spec. With rearward motion halted by the VIS, the [0.010 inch] or so of slack in the link system allows link tension to be relieved as the barrel drops straight down. All this in a mid spec gun.

The complete calculated "specification" for the distance between the barrel and the bed at first contact (link in tension) is 0.010 +/- 0.020 inch. Because the minimum limit works out to -0.010 (yes, minus 0.010 inch) it implies the barrel is below the bed. As this is physically impossible it means the barrel hits the bed first while the link is in tension, the feet never touching the VIS (until the link breaks)!

1911's in the lower 25% of the calculated tolerance band will thus exhibit initial contact with the bed. How many USGI 1911's actually fell into this category? It was probably very, very few - considering all this involves 12 tolerances on the 5 gun parts involved.

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...The key seems to be that the link is in tension when the barrel (its feet or chamber bottom) makes first contact with the frame - like Schuemann says...

The link is in tension as contact occurs.

But there 2 keys to this link-in-tension-first-contact...

To pass the Schuemann test... the barrel lower lug must make first contact, which has to be high up on the lug (near the barrel, not at the feet)

AND the barrel upper lugs must be completely clear of the slide by .015", again, while the link is still in tension.

Of course the tension will then immediately be lost assuming the VIS is hit first. That's ok.

Hope I'm not restating the obvious.

Feet?

Hi GBW: Maybe my terminology has been bad. I thought the barrel's "feet" and "lower lugs" were the same thing - the entire portion below the cylindrical part of the chamber. Are the feet just the bottoms of the lower lugs?

Let me know and I'll go back and edit my stuff. Thanx.

LOL - well, hmmm... that's a very good question, now that you ask it.

I've always thought of the 'feet' as just the bottom half, or thereabouts (from the slot down). Hitting the feet on the VIS - bad. Hitting the upper half of lug, closer to barrel the better, on VIS - good.

But that sure doesn't make me right - maybe someone else (Mr. 1911Tuner) can define it better for all of us!

Also, if you ever get time, 'cause it will be a lot of arithmetic, I'd like to know if it's even possible to get Schuemann's .015 in-tension clearance and his other specs using mid spec parts. I'm betting no.

You may be the only guy that understands the specs well enough to figure it out definitively.

Hi GBW: Now you got me to thinking about my use of the term "VIS". My (only) 1911 is a WWII-vintage GI model that has a distinct "bow tie" which extends about 0.010 inch forward of the flat bottom of the hole below it. My receiver "blueprints" are fuzzy copies of scans of original Ordnance Dept ones. They show this bow tie, but I can't decipher how far (if at all) it's supposed to protrude forward of the surface below. One place seems to show it 1/16, but another place on the same print seems to show it as ".005 -.005", implying zero protrusion (a flush surface) is allowable.

I recall reading somewhere in this forum that some guns don't have a bow tie, so for these I guess the VIS extends from the bed down to the bottom of the recess for the barrel lower lugs, a vertical distance of about 1/2 inch.

Anyway, the bow tie is what I refer to as the VIS. I always thought the area below it was recessed a bit to avoid the possibility lower lug contact too far down.

Hi N: I confess I don't know either. To me the VIS is the entire surface, but you have a point. And with your definition, the feet hitting the vis would be pretty much a non-issue, provided a dead flat end mill cut for the lower portion. (There is a set of receiver drawings on one of the CNC gunsmithing

sites, I think, but they may be the ones you already have.) My Caspian frames have a bow tie cut and the Essex don't. Not sure about commercial Colts - I have 3 older S70s, I'll check them tomorrow. I don't have any newer Colts or other manufacturers. As for the originals, I'm just not sure.

In any event, only the uppermost part of the lower lug should hit the vis to minimize rotational shock on the lower lug. Clearly the bowtie, when it exists, will insure this.

Also, the bow tie cut imposes a limit on the contact area - whether that's significant or not, and whether that smaller area is subject to setback by peening over hard use, which could change the timing somewhat, are also questions.

In Post #80, this thread, GBW wondered if it was possible to obtain the 0.015 inch minimum clearance between the barrel and slide when doing the Schuemann timing tests on a mid-spec M1911. For this test, the slide is about .25 inch out of battery, the barrel pushed fully rearward and the barrel aft forced upward to place the link under tension.

Dimensions and tolerances from Army Ordnance (Springfield Armory and Rock Island Arsenal) blueprints were used to make a series of calculations leading to the barrel/slide clearance under these conditions. The only assumptions made were:the barrel axis was parallel to the receiver top; the barrel link pin was a press fit with no change in its diameter; the tolerance for the .278 standard link was +/- 0.001 inch.

The clearance worked out mathematically (rounded to 3 places past the decimal point) to be 0.010 +/- 0.020 inch. Mid-spec clearance twixt barrel top and slide is thus 0.010 inch, which is 0.005 less than the minimum of 0.015 inch specified in the Schuemann timing tests.

Note that the minimum-spec clearance works out to be -0.010 inch. This implies the barrel upper radial lugs are that far away from disengaging from the slide. However, because the math involved about 16 different individual specifications (dimension and tolerance) among 6 different gun parts, the chances of any gun having a tolerance stacking problem like this are probably quite slim.

The chances of Niemi24s making a misteak are, however, not quite as slim. Went over the stuff twice, but it sure would be nice if somebody'd volunteer to independently check my work. All that's needed is a set of blueprints & some algebra and trigonometry skills. Any takers?

After 3 weeks of digesting all the sage info in this thread and connecting it with Schuemann's timing test instructions (barrel fully rearward and AFT END UP) the little light finally came on in my head.

In Post #1 I said a mid-spec GI 1911 would have it's downward motion halted by the bed. Tuner said that's OK as long as first contact is made with the VIS (which halts rearward motion). The key seems to be that the link is in tension when the barrel (its feet or chamber bottom) makes first contact with the frame - like Schuemann says. Ahhhhh, honorable masters, grasshopper finally get big picture.

So, how far is the barrel bottom above the receiver bed when VIS contact is first made in a mid-spec USGI 1911? After getting reliable specs for the link, it worked out mathematically to a tad more than 0.006 inch at mid-spec. With rearward motion first halted by the VIS (with the link in tension), the 0.010 inch slack in the link system then allows link tension to be relieved as the barrel drops straight down 0.006 inch to the bed, leaving the link loose (and 0.004 inch away from being in compression). All this in a mid spec gun.

Oddly, the max-spec distance was almost 0.027 inch which seems (to me) too much to even allow the barrel to unlock from the slide!

Odder yet, the min-spec distance was a tad more than -0.010 inch. That's negative 0.010, indicating the barrel's mathematically below the bed - a physical impossibility. This must mean the barrel hits the bed first, while the link is in tension, and the feet would never touch the VIS (until the link breaks)!

Encountering either the max- or min-spec situation would require about a dozen dimensions on 5 parts all at one tolerance extreme or the other. IMHO, the probability of this occuring is about the square root of zero point diddly squat.