I just finished a build on my friend's Springfield and installed a hard fit Kart barrel. I was able to get maximum vertical lug engagement in the area of IIRC .054" (I'm at work)
I thought that was good, but then I noticed something and in looking back at others' postings on their builds, it seems to me that there is a trend.
Fitting the barrels to max. vertical lug engagement (over .050") seems to create the following side effects:
- Firing pin striking low
- Need for longer barrel links (+.009" in my case)
- Longer link = slower barrel drop
- VIS needs to be moved back
- Frame beds need to be lowered
- Barrel ramps need to be recut because they are too close / overhang the frame ramp
This leads me to my question. What is really to be gained by increasing vertical lug engagement past .045" or centering the firing pin on the primer?
It seems that the cost of maximum vert. lug engagement is a lot of other things that if done wrong can really mess up a 1911. What is the practical difference between .045" and .050+" of lug engagement?
CONTACT. A hard fit barrel is one that makes contact on both feet on the pin and upper lugs make contact in the upper lug engagement, along with a snug bushing and you get a repeat barrel lock up position.
Getting an accurate upper lug engagement dimension can be awkward. If the barrel is making contact with the slide then the amount of engagement is limited by the first barrel lug recess. That's an easier one to get and I would be surprised if it's over .045".
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It seems that the cost of maximum vert. lug engagement is a lot of other
things that if done wrong can really mess up a 1911.
+1 for this.
Especialy when considering that while the maximum possible lug engagement (based solely on the heights of the slide & barrel #1 lugs) for a mid-spec USGI M1911A1 is 0.0595 inch, this gun will have only about 0.393 inch of actual engagement with a standard 278 link!
This 0.0393 inch engagement assumes gravity has the oportunity to lower the barrel a little over 0.003 inch after the link passes vertical on the way to battery (this gun does ride the link all the way into battery).
There may be some good reason why there's this 0.020 difference. Only thing I can think of it allows for the accumulation of 0.020 inch of crud - not an unusual consideration in a combat weapon design.
The other aspect you mentioned that's always had me puzzled is the need to move the VIS back and lower the barrel bed. JMB's design (as reflected in the blueprints in our Tech Issues section) fails the Schuemann timing tests - and fails them badly! With the barrel fully aft against the VIS and down on the bed, there's only a bit more than 0.008 inch of clearance between the top of the barrel and the bottom inside of the slide!
And to get the clearances called for by Schuemann, the VIS has to be moved back 0.010 inch and the bed lowered 0.025 inch - putting them both out of spec!
All the above based on a mid-spec USGI 1911.
In short, can't really answer your questions. I too await enlightenment from the wiser gun plumbers.
What niemi24s says about M1911A1 barrels is correct as the barrel lug recesses where cut on a .285"-.290" radius which makes the recess deeper than the NM standard of cutting the first lug recess on a .302"-.307" radius thereby allowing the barrel to make contact with the slide and not go too high as the older M1911A1 barrels would.
It was a common practice to weld a pad in the recess of the std. barrel so it wouldn't have to go so high to make contact. I find that the first barrel lug recess to be between .040"-.045" on NM barrels.
I've never fit a hard-fit barrel, but I have fit a couple of Kart Ez-fits; they have central firing pin strikes, full lug engagement on top, and they ride on the slide stop pin, on a standard link. If the slide and frame are properly dimensioned, I'd think you should be able to accomplish the same thing with a hard-fit? As niemi noted, the first barrel lug should be shallow enough that you get 100% engagement at the top, and if anything, you should have to remove a bit of material there to fit the barrel between the slide lugs and the slide stop pin.
Don't really see where niemi said that but it is correct regardless.
The key to unraveling this mystery lies in understanding that what stops the barrel's upward rise into the slide is the slide lugs bearing on the barrel between its lug recesses.
If the slide sits high, the hard-fit lower lug will lift it higher until it stops. If the barrel was cut on a .302 radius, it will require more material be removed from the lower lug and the barrel won't move up as high relative to the breechface. If it's cut on a .290 radius, it will require less material be removed from the lower lug, and it will sit higher relative to the breechface. Depending on how much tolerance stacking is present, the firing pin strike will be high or low.
Another issue that crops up once in a while is the slide lugs being shallow, letting the barrel engage vertically until the barrel lugs butt against the slide lugs' recesses. Once in a while... you get both issues.
The need for a long link is a clue here. If the slide lugs are bottomed on the barrel, it indicates that the slide is sitting high on the frame rails. This could either be due to frame rail/way mislocation... or slide rail/way mislocation... or a tolerance stacking situation in which each part is just within spec, but both together throwing the subassembly out of spec.
.005 inch too much vertical engagement wouldn't be too hard to cure, but it requires hammering on the frame to the point of actually crushing the ways, and cutting the bottoms of the ways to lower the slide. Much more than that isn't recommended unless you've done it a lot. I don't like to go much more than that... although I have on a couple of occasions. Very labor intensive and tedious, and also usually requires taking half the amount required off the slide... and being careful not to thin the slide rails beyond minimum... and deepening the disconnector slot, etc. When you lower the slide, generally everything has to be adjusted to compensate. It can get tricky, and I generally only do it when the gun is otherwise worth the effort... and I've got time on my hands anyway. I've only done extensive hand work like this on two guns that weren't mine. One was for a very good friend, who was at his wit's end with it. I put almost 20 hours into the gun before I got it squared away... 16 of which were spent on the frame and slide alone. So... Unless you've been into one like that... I don't recommend it.
Sounds like you might have one about like that...
I feel yer pain.
A better, but more expensive route would be to let George Smith have it to weld the frame rails and recut them...and then refit the slide to the frame at the proper height. He can likely refit the barrel while he's at it.
Last time I talked to Mr. Schuemann, I was going to ask about the VIS issue, but forget. I am thinking the clearences are for feeding, maybe to keep the bullet off the barrel ramp. Lower frame bed= lower barrel=lower barrel ramp in relation to round entering the chamber.
I was wondering if the I can ask more specifically, questions about the OP's original post, to clarify some points in my head, and perhaps his.
He mentioned all of the associated possible problems, and the thread has gone in that direction, as to an out of spec gun. What if the gun passes all of the appropriate timing and fit tests, and appears to be functioning well, is there an issue with:
1) Lower primer strikes
2) Any functional issues that may perhaps be related to longevity of the gun, etc.
Specifically, I recall reading in several posts (sorry I cannot find them) that a rough check for lug engagement is the popsicle stick method, whereby measurements are made to roughly check engagement. I also recall a specific thread whereby the lug engagement values were discussed. Take the lug engagement, multiply by two, and this gives a rough percentage of lug engagement. I also recall this thread gave percentages and gun use, with low percentages being recommended to be shot less, and other values as being safe with plus P, etc.
With 0.050" enagement equalling roughly 100% enagagement, is there an advantage to going higher, or perhaps a downside, if the guns is fit properly and functions?
I don't think this is an issue about an out-of-spec pistol. I think what Niemi said is the closest to what I'm questioning. The slide lug recesses in an in-spec pistol are over .059" deep. That means you could possibly fit a barrel to that much vertical lug engagement whether or not the frame and slide are in spec, correct? And if you did so, you would certainly need to do all the other things I mentioned, yes? Moving back the VIS, off-center primer strikes, longer link, etc. etc. Unless I missed something, I'm not sure my original question was answered. What is the practical advantage of getting that much vertical engagement?
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The slide lug recesses in an in-spec pistol are over .059" deep... What is
the practical advantage of getting that much vertical engagement?
There may well be no practical advantage, but I myself don't know for sure.
IIRC, during the last year (or so) 1911 Tuner had a post in some thread in which he talked about XY inches (or percent) of engagement being OK for an occasionally shot gun, YZ inches (or percent) being needed for gun seeing hard use, etc.
I don't recall any mention of 0.059 inch (or 100 percent) engagement though.
Thanks for confirming that I had not lost my mind. I cleary remember that thread, as I measured all of my guns, shortly thereafter.
What really hit home was the percentages and Tuner's breakdown of what might be expected as useful life based on the numbers. I was also paying close attention, as I had never checked this dimension in any of my 460 Rowland barrels.
I honestly do not think that I could shoot any of my 45 ACP 1911's enough to destroy a lug/barrel, even with a .048ish number, but I could easily do that in short order with the Rowland.
I am with Tom, kinda wondering if everything is working well, and you can get a little more engagement, can this be bad for some reason that Tom did not post, or my pea brain cannot fathom at first blush. Something like too much first lug engagement, compromising engagement on the other(s) due to the angles involved? I am still not convinced an off center primer strike is necessarily bad. I had a combination of Les baer slide on a Springfield frame in 45acp that was greatly off center, and I never experienced any ignition problems. Not sure I could say yes or no to degraded accuracy due to off center strike. I did learn from that combination that when you mix and match frames and slides, prepare for some possible migraines.
I'd appreciate it if someone could direct me to that previous thread. Thanks.
I found this one from 2007. Is this the one?
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Originally Posted by niemi24s
Just seems like 0.038" is pretty skimpy engagement for lug #1 in a mid-spec
gun
(Tuner's Reply)
It is... if you intend to shoot the gun 25,000 rounds a year. If you figure
on replacing the top end every 6,000 rounds give or take... it'll do. I have
seen very few that went less than 040 inch vertical... and I've checked a
bunch of'em. Most seem to run in the neighborhood of .040-.042 inch, with
several WW1 models checking as high as .048-.050 inch... but it's a moot
point. The slides and barrels were soft. The engineers and the Ordnance people
knew that the lugs would beat themselves into excessive headspace... and
whenever that was gauged and deemed non-serviceable... they just replaced
everything that was needed to correct it.
My simple-minded approach tells me that there is no such thing as "excessive vertical lug engagement". I would consider a centered firing pin strike to be one of the main goals of a properly fitted barrel. If the barrel did not fit hard in the upper lugs, then that's the breaks. I wouldn't raise it up if the f.p. strike was already centered. Would you?
I think the confusion may come from the nominal vertical engagement for an ordnance spec gun. Those numbers do not imply that having more engagement is a bad idea. I'll just speculate that early ordnance spec guns were not intended to have hard fit upper lugs, because of the time needed to properly fit such a barrel.
Most modern barrels, and especially the NM barrels are made with extra lug material specifically so they can be hard fit in the vertical dimension. With a NM barrel, you expect to get a hard vertical fit at the beginning, with the barrel a bit low on the breech (f.p. strike too high). Then, the challenge is bringing the barrel up to center the f.p. strike, while keeping a hard fit at the upper lugs. Vertical engagement is then checked to make sure it is adequate. Did I miss the point?
Lemme see if I can find the right words...
If the barrel is touching the slide lug... fitted to it... then the slide lug's male corner will bear against the barrel lug's female corner when the gun is fired and the lugs are horizontally engaged under force. This provides a strong resistance to the shearing forces that are trying to rip the lugs off.
If the male corner is bearing on the center of the barrel lug face... not so strong. Imagine slamming two hammer heads together... off-center... as opposed to them being centered.
If the barrel is hard-fitted via the oversized lower lug to the point that it's vertically limited by the slide lug... and the firing pin strike is low... the slide is too high on the frame relative to the slidestop crosspin's centerline.
Only rarely will you see the barrel's male corner bear into the slide lug's female corner.
(Barrel lug front face to slide lug rear face.) Ideally, you want both corners inviolved so that both lugs offer the maximum resistance to shearing... but that rarely happens, and is hard to achieve unless the gun is hand-built from the ground up. Most of the time, what we get is slide lug male and barrel lug female, with clearance above the top of the barrel lug.
Look at the X-Ray picture on the recent sticky. You can see the clearance, even though the slide lugs are touching or nearly touching the top of the barrel forward of the lugs.
This is why a Kart Easy-Fit barrel isn't always the best option in pistols with slide height above the rail spec issues. You can use the pads to achieve a hard fit... but with too little lug vertical engagement... and the lug becomes deformed to the rear with use. The obvious sign of insufficient vertical engagement is a stair-stepped appearance on the front face of the barrel lug and flanging on the top. Because the slides are harder than the barrel, we rarely see corresponding damage to the slide lugs, but I've seen it a lot on older, soft slides.
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I found this one from 2007. Is this the one?
Yup, that's the one. Good job searching and finding this thread: http://forum.m1911.org/showthread.p...highlight=0.038 . It was easy for me to find using the first 4 words in your quote.
One concern raised here has been off-center firing pin strikes. Dead center seems the customary goal, but some guy at the range keeps saying an off-center strike is actually the best! Could never pin him down about how far off was the best or how far off was too much though. I'd think the primer manufacturers would have done tests to find out.
An off-center firing pin indent won't bother me, if the gun locks OK, up and down.
The strike that's vertically +/- .010 inch off-center is much ado about nothing except in precisely built pistols whose owners are chasing bughole groups at 50 yards. a horizontal off-center strike is a different matter... but vertically? feh
Tom, you did not mention if you attempted to get more than one upper lug in bearing. Even though lug #1 is going to have the most engagement, the others will contribute to the longevity of the barrel. A few measuring jigs for this job are shown in Kuhnhausen.
On this particular pistol, I had full horizontal contact with the first two lugs. The third was hanging off .004" so I didn't even try to bring it into play.
I think I haven't done a good job framing my question, though, so I'll try this.
The next time I'm fitting a barrel, and I'm filing the lug slots on the barrel to increase vertical engagement, when should I stop?
Do I stop when the gauge fits into the firing pin hole, as long as I have at least .042" or so engagement? Or, do I keep on filing until I get over .050"? When should I stop, because the more I file, the greater my vertical engagement, the longer the link I'll need, the greater the chances I'm going to have to move back the VIS, lower the frame bed, relieve the slide, etc. in order to get sufficient barrel drop.
How much vertical engagement is enough?
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The next time I'm fitting a barrel, and I'm filing the lug slots on the
barrel to increase vertical engagement, when should I stop?
When the barrel touches the first slide lug. For strength, durability, and longevity... you want the barrel lug to bear the horizontal forces low on the lug... in the corner. If the firing pin is a little off-center... don't sweat it, as long as it's not hitting on the edge. +/ .010 inch means pretty close to zip unless you're chasing half-inch groups at 50 yards... and even then, it doesn't mean much.
The other caveat is to make sure that you're getting full linkdown clearance at .250 inch of slide travel. Some barrels have tall lugs. Some barrels have ordnance dimensions between the lugs and some have larger, national match dimensions. .290 inch and .302 inch, respectively. Fitting a barrel sometimes requires a little here... a little there... a little in the middle... in order to get a precise fit. Again... that precise a fit isn't worth the headache unless the whole gun is precisely built. See Jerry Keefer for a tutorial on that. His pistols are stupid accurate. They also cost about 4 grand to build from the ground up. Mine will do to ride the river with. As much as I revel in pistols that will shoot like that, I don't have the time or the desire to mess with it... even if I had the required equipment. Life's just too dang short to worry over an inch at 50 yards with a pistol. I do good to see an inch at 50 yards... much less hit it.
1911Tuner
don't sweat it, as long as it's not hitting on the edge. +/ .010 inch means
pretty close to zip unless you're chasing half-inch groups at 50 yards... and
even then, it doesn't mean much.
This is true... and as Tuner says, not all 1911s or barrels lend themselves to ultra precision fit. I like as much contact in the upper lug area as possible, which stablizes the barrel while the gun is in battery, and the internal ballistic event is in process... remember, the slide is moving before the bullet leaves the muzzle. The more stable things remain during this time, the more accuracy you gain. If the frame/slide/barrel are match grade, the firing pin will end up reasonably centered. If it's too far off, it can be relocated with an offset bushing. Three areas of lug concern for super accuracy;
Full upper lug contact; maximum lower lug contact; and a link lenght that is in the mid to lower 80's. Long links, 90's, tend to have feeding problems. This was common in the old days of welded up barrels... and loose frame/slide tolerances.
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Because the slides are harder than the barrel...
The Ordnance Dept. barrel blueprint in our Tech Issues section specifies a hardness of "Rockwell 053 to 56.5" (I'd assume that's on the C scale), but a tour of the Brownells catalog shows 6 barrel manufacturer's giving hardnesses ranging from 38 to 43.
That's (on the average) a difference of about 14 RC's, and seems (to me at least) a really big difference.
Anybody know why the modern commercial barrels are so much softer?
Could it have to do with most of them being stainless steel?