I recently fit a Kart Easy Fit barrel to my Metroarms AC-II and shot 150 round last night. She shoots great.
While cleaning and inspecting the pistol last night I noticed that there is a lot of contact on the VIS of the barrel and frame but there are also rub/contact marks on the barrel bed. It is not clear to me if this is a concern?
I will post pictures after work today.
Is VIS and bed contact the best scenario or should I lower the bed a little (dowel wrapped with 400-grit until full bed contact is seen).
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...I noticed that there is a lot of contact on the VIS of the barrel and
frame but there are also rub/contact marks on the barrel bed. It is not clear
to me if this is a concern?
Contact with both the VIS and bed is ideal - and the VIS must get hit first. I don't think it's necessary that the barrel makes contact with the full length of the bed - provided there's sufficient clearance between the top of the linked down barrel and the slide and there's not too much gap between the back of the barrel and the bed.
Performing the linkdown timing tests from Schuemann Barrels (see our Tech Issues section) will tell you whether the barrel hits the VIS before the bed - and it's important contact is made in that sequence. If the bed gets hit first it can break the link.
Hello and thank you Niemi24s... I performed the Schuemann test using dyechem blue to learn that the bed and VIS hit about the same time . I noticed that the bed only had two small contact patches because of rough machining so I sanded down the bed a little with a dowel wrapped with 400 grit to match the diameter of the barrel. Now the VIS hits just a little ahead of the bed. I will learn more after the next range trip because I cold blue everything and look for witness marks after shooting. I hope that the new barrel VIS works into the frame and the VIS and bed bottom together.
All is good.
Anyone ever noticed that in Jerry Kuhnhausen's first manual, he says that the barrel should impact the bed and not what we now call the VIS? That makes me wonder if some of the old pistols weren't set up that way. He corrects this in his second manual.
Yes, I did after reading a posting from Tuner who pointed this out. I think that the old frames and slide weren't hardened like modern 1911s. Perhaps this is the reason but I can't think of why. Kuhnhausen vol-I goes as far to state "full bed contact".
What I've done on the few pistols that I've tinkered with is this: I remove the recoil spring plug and with the gun assembled, insert a pencil or dowel into the barrel and hold up on the chamber end while pushing back on the barrel, making sure that the link pulls the barrel away from the slide .010" or more. Then push the muzzle against a solid surface untill it stops and check to be sure that the slidestop pin will swing free. Basically the same test as Schuemann's, but without his tools.
Oh, the first part of that is done with the slide open about a quarter inch, of course.
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Now the VIS hits just a little ahead of the bed.
That's good!
That means the VIS is halting the barrel's aftward component of motion. After hitting the VIS, link tension is immediately relieved as the barrel (no longer moving aftward) drops down to the bed.
And there's no reason to try to get the barrel to hit the VIS and bed simultaneously. That condition is too close to having the link halt the barrel's aftward component of motion - which can break the link.
Will break the link, or the link pin, or the slide stop. OR pull the foot off the barrel. One brand use to cut the foot with a square corner endmill and I have seen several that pulled the foot out the bottom of the chamber. Not a pretty thing.
Hit the frame VIS first, than best to have a little wiggle room to keep the barrel from bouncing up. Maybe .005 up and down.
I like the no spring test with the rod in the barrel barrel pushed back against the VIS and see with your thumb if the barrel has a little wiggle up and down.
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I like the no spring test with the rod in the barrel barrel pushed back
against the VIS and see with your thumb if the barrel has a little wiggle up
and down.
Hello and thank you for the recommendation George. The simple test you described sounds like it will shed more light on the new barrel fit... thank you.
I thought that all barrel manufactures put a stress relief on the block-to- barrel interface but after your comment I think I will look more closely at mine.
Edit: The Kart has generous stress reliefs...
Just a quick comment on the barrel hitting the bed lightly or just barely behind the VIS. It may be okay for occasional, light use... and the average shooter who goes through a box or two a year will probably never see any trouble. But... as the gun becomes fouled and the gap between the barrel and bed closes up... it will stress the link and do what George describes. I've seen lower lugs pulled off the barrel. A couple pulled clear through the chamber. If it hadn't been caught in time, it coulda gotten real ugly real quick.
pardon my ignorance, but what is the acronym VIS being used for ?
VIS = Vertical Impact Surface
Dead, it's the vertical surface in the frame just ahead of the curved barrel bed. The barrel's rearward movement should stop on that surface with just a little clearance between the bed and the bottom of the barrel. It doesn't have to be much. .003 inch will do... but it has to be there. I prefer just a little more to allow for heavy carbon fouling in my range beaters. I tend to shoot upward of 250-300 rounds per session per gun with cast bullet reloads... which dirty up the area faster.
Additionally, there's another barrel clearance at the point of that impact, and it has to be at the right time. With the slide 1/4th inch out of battery, the barrel should be stopped against the VIS with .015 inch of clearance between the top of the barrel and the bottom of the first slide lug. That clearance must be achieved by the link. Pushing the barrel down to get the clearance doesn't help. It's checked with the barrel against the VIS with the slide .250 inch rearward, with all play removed from the link... usually done by levering the barrel up as far as it will go. One test kit uses a spring, but as long as the slack is removed...either one will do. If the barrel moves freely, it can even be rough-checked by holding the pistol upside down to see if the clearance disappears. Another quick check is to simply press the muzzle against the edge of a heavy bench briskly as far as it will go and looking for the clearance. That traps the barrel so that it can't drop from gravity when it's firmly against the VIS.
It serves as a quick-check/field test, to see if there's an obvious problem. In a gun shop... looking to buy... it can be done by pressing the muzzle straight back with your hand. It won't determine if the barrel is being stopped by the link, though. That requires removing the slidestop and doing the free-swing test.
Not sure who this Tuner fella is?
One of the issues with a "production" gun is getting this correct.
Barrel does not hit VIS, barrel, link, link pin, slide stop break. Gun goes bk to MFG. Next day air.
Link does not pull barrel out of top lugs, lugs roll off and peen. Gun goes back and slide and barrel need to be replaced and or gun does not eject, stalls etc.
If the clearance between barrel and slide gets TOO large the barrel drops down so much the case is at the bottom of the extractor hook that is not centered on the case when Out of battery and ejection problems can show there ugly heads.
1911 is not the easiest gun to mass produce. A Glock, S&W barrel that is linkless is easier to mass produce. Maybe something to do with the less expensive guns not being the most reliable?
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Not sure who this Tuner fella is?
Just an old mechanic, George.
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Link does not pull barrel out of top lugs, lugs roll off and peen.
Dead... to expound on this point:
When the barrel stops flat against the VIS... if the upper lugs are still engaged... even a tiny bit... the slide keeps moving. The barrel is trapped between the slide and frame by the rear face of the lower lug, and the front faces of the upper lug corners. The crash will eat the upper lugs off the barrel like right now. It doesn't do the slide lug corners any good, either. It can also crack the lower lug adjacent to the barrel at the rear. Bad JuJu any way you look at it. This is one reason why long-linking a barrel to get better "lockup" is a bad idea. If it's too long to time the barrel drop, the lugs don't get completely clear of the slide.
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If the clearance between barrel and slide gets TOO large the barrel drops
down so much the case is at the bottom of the extractor hook that is not
centered on the case when out of battery and ejection problems can show there
ugly heads
The red flag for this one generally shows up as weak ejection on the last round with a flat magazine follower. As long as there are rounds under the extracting case, it can't drop any lower than the surface of the next round. When there's nothing to keep it up on the breechface... when the magazine is empty... it drops. In extreme circumstances, if the extractor is really working... the last empty case can actually be stuffed partway back into the magazine. The slide doesn't lock, and tries to feed the empty case... and the case gets the telltale 2-point crunch at the mouth.
A clocking extractor often mimics this one... so check both before you assume that the frame bed is too low.
Little things that make this old pistol so interesting...
I just checked my Caspian build where I used a Kart barrel that I hard fit.
With just the slide, barrel and bushing I get .018 clearance between the top of the barrel and bottom of first lug.
With slide assembled on frame I get .008 clearance when the barrel is pushed back and down at the muzzle. The ss pin is installed and the recoil spring is not while testing.
So, is my VIS too far forward or the barrel bed too high, or a little of both?
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So, is my VIS too far forward or the barrel bed too high, or a little of
both?
The answer to that, unfortunately, depends on who's doing the answering.
So who are you going to believe? That's up to you. Consider this, however: If an average, mid-spec Gov't Model M1911A1 is put together following the Schuemann Barrels instructions:
Hopefully, other Forum members will weigh in with their learned opinions and help you decide what to do.
That sounds like the guide rod flange is holding the barrel off the bed.
I came up with .008 without any guide rod or recoil spring installed. Just the frame/slide barrel/bushing and slide stop. Barrel was pushed up and rearward.
I just measured the depth of the barrel bed and it is .064 from the top of the frame to the bottom. Is this maybe a little shallow?
The bed couldn't be too shallow if you're gettin' .018" clearance when the barrel is just lying on the bed, which is what you said if I understood it right. .008" would be enough for me; however that could lessen in time if the link streched or the SS pin wore, don't know how likely that is to happen. Only way to increase clearance with tension on the link is use shorter link or move the VIS back, and both of those things change other things, which could be important, such as ramp to ramp gap, lug engagement and possible binding of the lug feet, SS pin and barrel link.
I measured .018 with the slide off the frame and just the barrel and bushing installed.
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It doesn't have to be much. .003 inch will do... but it has to be there. I
prefer just a little more to allow for heavy carbon fouling in my range
beaters. I tend to shoot upward of 250-300 rounds per session per gun with
cast bullet reloads... which dirty up the area faster.
Hello and thank you for the great advice Tuner.
I removed a wee-bit more material from the bed for extra clearance. I used the .25" out of battery without a recoil spring and pushing the barrel down and back method to determine that there is wiggle room between the barrel and bed. I can use .003 paper for shims to try to get a measurement in .003 thou increments later but if I had to guess I have .003-.006 clearance.
Ben- Oh, right. Thought I must have missed something judgin' by Tuner's reply.
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I just measured the depth of the barrel bed and it is .064 from the top of
the frame to the bottom. Is this maybe a little shallow?
Yes.
The derived spec for that distance is 0.077 +/- 0.005 inch.
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The derived spec for that distance is 0.077 +/- 0.005 inch.
According to my blueprint, it would be 0.077 + 0.005. No minus.
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According to my blueprint, it would be 0.077 + 0.005. No minus.
Here's where the minus in the tolerance comes from:
(0.450 - 0.005) - (0.373 - 0.005) gives extreme values of
Max = 0.450 - 0.368 = 0.082
Min = 0.445 - 0.373 = 0.072
Avg = 1/2(0.082 + 0.072) = 0.077 and as that's 0.005" from (and in between) the Max & Min values, the bed depth = 0.077 +/- 0.005 inch.
When two toleranced dimensions are added or subtracted, the tolerance of the result is always greater than the largest tolerance of the two - that's how tolerances "stack".
The bed depth on the blueprints is obtained from a radius shown on the end- on cross-sectional view in the approximate center of the sheet. That radius is 0.348" + .005"
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The bed depth on the blueprints is obtained from a radius shown on the end-
on cross-sectional view in the approximate center of the sheet. That radius is
0.348" + .005"
That 0.348" + 0.005" is only the radius of the bed - and nothing more. Note that the little "+" denoting the center of the radius is not dimensioned, but is merely shown as being on the frame's vertical centerline.
What does determine the vertical position of the bed is the 0.373" - 0.005" off to the right in that front view. That's the distance from the bottom of the bed to the center of the SS pin hole.
Those dimensions and lines are a lot easier to see in the Nicolaus book of drawing than in those in our Tech Issues section, where this is from: