I'm thinking about building a 1911 with as much vertical engagement as I can get (probably .060" to .065"), for the heck of it. I'm almost certain the firing pin strike will be low, and I'm not set up to peen down the frame rails to lower the barrel relative to the FP.
Does anyone on the market make off center barrel bushings that fix low firing pin strikes? I know they make firing pin bushings that raise the firing pin strike, but how about barrel bushings that sit the front of the barrel higher? I'm just considering all the options. Thanks in advance.
For the firing pin I'd contact Clarks.
They used to have something like that but I don't know if they still do.
Keunhaeusen cautions against to much vertical engagement, IIRC it has something to do with the barrel timing. You might want to do some research before getting started.
Maybe speak with a .460 Rowland owner? That one oughta lock up tight.
Yup. Too much is as bad as not enough. .050 inch is plenty. .045 will do nicely. If the lugs are horizontally equalized .040 is okay too...as long as the bottom of the slide lugs are contacting the top of the barrel. That's paramount if you want to avoid beating the barrel lugs back. You also want a little barrel tilt in battery, even if it means that the firing pin isn't perfectly centered. .010 inch vertically off-center is neither here nor there unless you're chasing 3/4-inch groups at 50 yards. If that's what you're after, save up about four large and give Jerry Keefer a call. You won't be disappointed.
The tilt means that the lugs are under angular compression from the top front toward the bottom rear of the lug when the forces slam into'em. If it's focused straight back, the number 2 and 3 lug are absorbing it with no solid backing, and they'll deform...or shear.
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Does anyone on the market make off center barrel bushings that fix low
firing pin strikes?
Never heard of such a thing, but EGW might be able to make one for you.
Only problem is you'd have to raise the muzzle about 0.007" for every 0.001" of pin strike lowering. Then, of course, there's all the stuff previously mentioned.
I remember someone making offset FP bushings. Tuner said Clark, maybe.
Thanks for all the replies! There's a lot of good stuff here to think about.
Joni and Berk, if I go that route, I'll try Clark first. Thanks for the info.
Toolman, I can see how having the barrel positioned higher in the slide could make barrel lug clearance from the slide difficult to obtain. The VIS may need to be moved back more than I'd like. (I'd like to avoid messing with the VIS at all).
Salty, I wonder how much more vertical engagement a .460 Rowland gun would have over a .45 ACP. Contact with all lugs horizontally is probably required. I'm guessing 10mm would need more as well.
1911Tuner, thanks for sharing. I learn something new about the 1911 everyday; this site and your contributions are the main reasons why. The relationship of the angle of compression and the lugs' resistance to deformation/shearing is very interesting, and one that I didn't take into account. It seems if I'm going to do this project, I'll need to get past the excuses and learn how to peen the frame rails. The barrel bushing method would change the angle of barrel tilt more than I'd like. For a workhorse/practice gun (maximum lifespan), how much vertical engagement would you recommend assuming equalized horizontal lug engagement?
Niemi, thanks for those numbers. I guess it doesn't make much sense geometrically to try and solve the low FP strike via the less efficient route, all the way on the far end of the barrel.
tophat, I simply do not know. I am the gent who managed to mis-fit a Kart E- Z to the second lug.
Mz Joni, bless her bones, suggested talking with some people at Clark. Those folks fit/sell 460 Rowlands, and will know something about containing pressure with fit.
A 460 owner may be able to offer some a bit non-commercial insight.
Jim, Sr. did install an offset firing pin and insert into my Sistema wadcutter pistol, circa mid-60s. It had been lowered.
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The relationship of the angle of compression and the lugs' resistance to
deformation/shearing is very interesting, and one that I didn't take into
account.
It's a point that most don't think about... including a few high-end smiths. It's also why that sometimes, the Kart Easy-Fit system isn't a good option.
Consider the small radial lugs that engage between 10 and 2. Assuming that all are equalized horizontally... there's not a lot of steel to absorb the recoil forces. Cut that down to just 2 lugs, and it gets even worse. If the fit doesn't bring the first, strongest lug into play... the gun is runnin' on a wing and a prayer.
It would have been easy for Browning to put the barrel into battery horizontally, and drop below that plane when the barrel links down. it would have made feeding much simpler... but he had to contend with those tiny lugs, so he tilted the barrel up into battery, placing them into angular compression... making them about 50% stronger than they would be if they took the brunt in a straight line.
Doubt it? Go find an early Norinco that didn't have good vertical engagement... essentially straight-line horizontal lug engagement... shoot it 500 times... and look at the lugs. Shoot it another 500 times, and check the headspace. Another 500 times... if it doesn't start bulging and/or bursting cases... and you're in the market for a new barrel.
I saw a Kart easy-Fit installed in such a pistol once. Over half the fitting pads remained. I pointed the condition out to the so-called custom smith who built the gun, and he said that it didn't matter... that it could "lock anywhere on the arc." At that point, I figured there was no sense in trying to convince him of something that he already had his mind made up about... grinned, and walked away.
Not only was the vertical engagement less than optimum, but the lugs were horizontally engaged straight-line between maybe 11 and 1. That makes Billy's breech very weak.
I assembled a gun using a Caspian frame and slide with a Kart barrel. In order to center the firing pin, I wound up with at least .060" engagement; I think it is closer to .070".
It took almost all the 'meat' on the lower lugs to raise the barrel that high and still have slidestop pin contact.
Then it took a King's #13 link. Don't remember the exact dimension between the holes, but it was well over .300".
With the long link, I had to move the barrel stop surface on the frame back to allow for linkdown.
With the stop surface back, the barrel had to be ramped that much farther forward for the frame to barrel gap, which lost case support.
Guess I could have lowered the rails to keep from using such a long link, but then I'da had to lower the frame bed, and the gun feeds too 'slick' the way it is.
I get along OK with it, but I would put it off on ya if I could . For long life and retaining pressure, I think that equalized lugs bearing the way Tuner was talking about and with the hood fit to minamalize forward and aft slop is all anyone needs.
Hi Barry, so in your case, you needed to raise the barrel relative to the slide to center the FP? That's interesting. I may have to use a Caspian frame and slide combo. What is the distance from the FP hole in the breech to the slide rails?
As for moving the VIS back, I'd like to avoid it, but with that long of link, I can see why it was necessary.
I don't understand why you needed to remove case support to get the barrel to frame gap though. Let's say the corner where the top of the barrel ramp meets the chamber is point A. The bottom corner of the barrel ramp is point B. Point B vs the top edge of the frame ramp should have a small gap around .030". If not, point B may be moved back to gain the gap. The barrel ramp angle may become more vertical as a result. Moving Point A should be unnecessary (save maybe for only the most extreme barrel overhang), and removing material from point A will lessen case support.
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Doubt it? Go find an early Norinco that didn't have good vertical
engagement... essentially straight-line horizontal lug engagement... shoot it
500 times... and look at the lugs. Shoot it another 500 times, and check the
headspace. Another 500 times... if it doesn't start bulging and/or bursting
cases... and you're in the market for a new barrel.
If I happen to run across an early Norinco in stock condition, I'll check it for lug damage. Otherwise, it's highly unlikely I'll try this test. No point arguing with what you're saying, since it makes a lot of sense.
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Yup. Too much is as bad as not enough. .050 inch is plenty. .045 will do
nicely. If the lugs are horizontally equalized .040 is okay too.
So I broke out Sweeny last night, and he recommends a minimum of .055, measured by smoking the lugs, setting the barrel in the slide, and tapping with a mallet.
His fitting method is:
1) fit hood (sides and length, using EGW length gauge)
2) File down fitting pads/bottom of lug until at least .055 engagement is achieved, measured as above
3) Grind/file on lower lugs until slide moves all the way into battery
4) Pick link based on distance between hole and lower lug/stop pin contact surface
5) Round off lower lug knees so that slide stop pin clears
6) Enjoy your new barrel.
I'd have to go back and reread Keunhaeusen again to be able to say precisely what he says, but it's something to the effect of the more vertical engagement you can achieve the better accuracy you're likely to have, but when you exceed something like that .055" number you are running a severe risk of timing problems. The corners of the barrel lugs and slide lugs will begin crashing into one another while the barrel is trying to unlock from the slide. Or something like that. You'll definitely want to look into that before trying to exceed the numbers 1911Tuner has given us.
I would abandon this project and just build a 1911 the right way.
Go for 100% horizontal engagement, and try to get your firing pin centered on the bore with .040 -.050" of vertical engagement. Any more won't help and will only give you problems with timing and durability.
Every frame ends up with a "sweet spot" regarding the relationship between the slide, frame, and barrel where you'll have sufficient vertical engagment and you won't have to move the VIS back any. Every .001" of vertical engagement past this point will force you to move the VIS back .0007". You'll then need a longer link which will slow down the timing of the unlocking phase. You may then need to lower your frame bed, which will shorten the feed ramp and change the feed geometry. You may then need to move back the barrel's ramp and reduce chamber support. You may end up with too-short of lower lugs on your barrel too. This will prevent the barrel locking up tightly on the slide stop pin. It may also prevent you from actually getting the vertical engagement you were trying for. You may also end up with insufficent "meat" on the lower lug legs, which may deform or shear off eventually.
The point is that the 1911 was designed to operate WITHIN tolerances. Deviating from those tolerance, either way, carries consequences which often negate the purpose of the deviance in the first place. And make you do a lot more work.
Toolman and Tom, thanks for your advice. I know exactly what you are saying, and in the past, I have had to make all of those modifications to the frame to get enough barrel clearance. It's definitely not preferable to alter the frame, especially the VIS, but this project isn't to build a typical 1911, which I have before. However, your tips do make me want to delay the project until I learn how to lower the frame rails (essentially eliminating the timing problems with long links). I will still have the barrel angle problem, however.
About the tolerances within the design, I do understand that altering it will change the system and require more alteration that initially planned. In fact, the initial plan may change as the project goes along. That's the cost of doing unique things like going for 0.060" engagement. Worst comes to worst, I'm out the cost of barrel when I discover exactly how much I need to move the VIS back and decide not to. There will be more of them, new surprises and issues like the angular compression on the barrel lugs. I'm willing to lose some to gain some, even if gaining here is only further education about this beloved 1911 design.
Tophat... As near as I could measure with a standard caliper, from the top of the firing pin hole (all caspians are .38 super firing pins) to the bottom of the slot in the slide was .545 to .550. It's the only Caspian slide I've ever seen; guess that they are all the same.
Sweeny's method doesn't account for lug equalization, which would be worth more than engagement in my opinion. I did it the same way as RobL quoted him except I concentrated on centering the firing pin instead of worrying about lug engagement.
I tried to measure the engagement again. I don't have a mic to measure it exactly, but don't believe that it is as much as I first posted. Looks to be about .060" or a little deeper at the first lug. Don't think that #3 is bearing.
Kuhnhausen says you should make it rule not to expose more than .090" brass in front of the case bevel, taking into account the barrel going forward and the case backing out against the breechface in firing. This gun exposes near .010" more than that. I've put over seven thousand rounds of full power ammo thru it, loading cases untill they split, and have never seen any bulged brass, so the limit must be conservative.
If I ever rebarrel it, I know that I can keep it in that limit. The frame to barrel gap wouldn't have to be as much, the barrel ramp could probaly be a little steeper as you mentioned and I wouldn't break the top of the barrel ramp hardly at all.
Thanks for measuring your slide. That is a good point with the horizontal lug engagement. I think most production slides and barrels don't have engagement across all three lugs, so maybe Sweeney is erring on the safe side with his suggestion of the vertical measurement.
By the way, in addition to the amount of brass exposed rear of the chamber, the headspace also contributes to the problem. So if your gun has .100" of brass exposure but minimum headspace, you could still be fine. If you have .090" of brass exposure but near max headspace, problems with case support may arise even though you meet Kuhnhausen's suggested specification. Another issue is this, if the headspace is near maximum, is the barrel shoulder too deep, or is the headspace at max with the rear end of the cartridge sticking out? If the shoulder is deep, hopefully that means there is still enough case support. If the shoulder is shallow, but the gun is near max headspace, bulging or worse is bound to happen. This is why we must remain vigilant and be constantly looking for signs of case bulging.