1911 tolerance stacking

[W.R.Buchanan]

Unclebill: I hope you read my dissertation on "Stacking of Tolerances" in post #8 that took me an Hour to write?

After re reading your OP I understand what you are saying and what you are describing is similar to stacked tolerances, however what it actually is,,, is the result of a single part with multiple features made to opposite ends of tolerances. IE: one feature of the part (OD) to the minus side and one feature (ID) to the plus side. Unless this part just wore itself to these dimensions?

If you got a tighter bushing your gun would probably shoot better What I read above was entirely too loose. You have three parts that are not matched to each other, but the bushing is the primary offending item. The OD is too small for the slide and the ID is too large for the barrel. Getting an oversized or maybe just a correctly sized bushing, would probably improve it's accuracy dramatically.

In order to shoot accurately, any auto pistol must index the barrel to the slide, or more properly the sights ,,, the same way every time. On a 1911 the barrel is indexed to the slide by the fit of the locking lugs, and the barrel bushing. The link, when fit tight, will actually push up on the slide taking some of the slop out of the slide rails when in battery. This helps to insure that the rear end of the barrel returns to the same place everytime the gun is cycled.

The bushing locates the front of the barrel and if it is not tight or very close then it will flop around and not positively locate the barrel on the front end resulting in the gun shooting to a different place every shot even though the Point of Aim has not changed.

This is the simple explanation . If the two features above are correct or even close then the barrel's inherent accuracy is the only variable that is left.

Randy

[unclebill]

Unclebill: I hope you read my dissertation on "Stacking of Tolerances" in post #8 that took me an Hour to write?

After re reading your OP I understand what you are saying and what you are describing is similar to stacked tolerances, however what it actually is,,, is the result of a single part with multiple features made to opposite ends of tolerances. IE: one feature of the part (OD) to the minus side and one feature (ID) to the plus side. Unless this part just wore itself to these dimensions?

If you got a tighter bushing your gun would probably shoot better What I read above was entirely too loose. You have three parts that are not matched to each other, but the bushing is the primary offending item. The OD is too small for the slide and the ID is too large for the barrel. Getting an oversized or maybe just a correctly sized bushing, would probably improve it's accuracy dramatically.

In order to shoot accurately, any auto pistol must index the barrel to the slide, or more properly the sights ,,, the same way every time. On a 1911 the barrel is indexed to the slide by the fit of the locking lugs, and the barrel bushing. The link, when fit tight, will actually push up on the slide taking some of the slop out of the slide rails when in battery. This helps to insure that the rear end of the barrel returns to the same place everytime the gun is cycled.

The bushing locates the front of the barrel and if it is not tight or very close then it will flop around and not positively locate the barrel on the front end resulting in the gun shooting to a different place every shot even though the Point of Aim has not changed.

This is the simple explanation . If the two features above are correct or even close then the barrel's inherent accuracy is the only variable that is left.

Randy

i read it alright
over and over again.
the only reason i posted all those pics is i figured the more information i impart
the better you can be informed as to what is happening without being able to inspect it in person.
thank you so much for the time and thought you have shared.
bill

[W.R.Buchanan]

Sorry for the extra post,,, the site is acting weird.

A good friend of mine, a guy named Mike Tibbet, who was a prominent Bowling Pin gun builder Back in the 80's solved this lock up problem in a unique way.

When he installed a compensator on his guns, the barrel would have a large tapered section about 2" long and 7/8" in dia at the big end right in front of the compensator. The slide was bored out to match the taper on the barrel. The bushing was eliminated.

As the slide recoiled the link would lower the locking lugs out of battery just like they do normally and the clearance necessary to accomplish this was delivered as the slide opened and the mating taper on the barrel opened up.

As the slide closed the barrel would go into battery just as the slide was closing and when the slide was all the way closed the taper in the slide was mated up to the taper on the barrel and there was ZERO slop. It repeated every time it was fired.

The taper was responsible for indexing the barrel to the slide and the fit of the locking lugs was much less important due to the length of the taper.

I actually saw him shoot a 1" 10 shot group at 50 yards with one of his .38 Super guns.

I would also tell you he did it offhand, but you probably won't believe me. I know I didn't believe it and I was standing there next to him.

I have the tool he used to cut the female taper in the slide in my shop I realize this doesn't really apply to your specific gun but it will help understand how the whole system works and that there are other ways to accomplish what Browning originally set out to do.

Randy

[Mik]

i have a GI1911A1 springfield and it never was a target gun.

End of story IMHO.

What you have there is a 1911 the way it was intended to be.

If you want a race gun, you'll be better off buying one flat out.

[unclebill]

End of story IMHO.

What you have there is a 1911 the way it was intended to be.

If you want a race gun, you'll be better off buying one flat out.

nope
the end of the story is when the groups tighten up enough to hit an 8" clanger at 10 yards.

[Mik]

nope
the end of the story is when the groups tighten up enough to hit an 8" clanger at 10 yards.

Yikes, I had no idea it was that bad. I would have guessed 4 to 5 inches at 25!

[220swiftfn]

As someone else already mentioned, a call to EGW with your measurements will probably get you to where you want to be for the lowest reasonable cost. Barrel to bushing and bushing to slide fit are the MOST important to accuracy, fitting the hood and feet are lower on the list (they DO help, but that doesn't sound like what you need for your use.) There was an article that mapped out what improvements made what accuracy differences (damned if I can remember WHERE tho....) but across the board the most dramatic was fitting the bushing...


Dan

[jmsj]

unclebill,
I checked the EGW site and they do make a .705" bushing that can be bored to the specs of your barrel.


jmsj

[unclebill]

thanks SO much for all the help you guys.
i am going for that bushing.
and i am ashamed to say it
but never once have i completely stripped this gun down to the last screw.
i will probably do that today.
detail clean it and use some sort of dry lube in judicious amounts.
thanks again guys!

[downzero]

I am enjoying reading the specs here and the discussion, but I also want to point something out: Springfield Armory has a legendary warranty, and they will take your gun back at their expense and pay an American to bring it into spec.

Take advantage! Send your gun back and have them go through it. You will get it back with better parts than it wears today, for sure.

[BD]

After reading through this thread, I believe you have a poorly fit bushing, and your barrel is "riding the link". I basically tend to agree with with Mtn Gun regarding long links, and I'm thinking yours is too long from the git go. The barrel link and bottom lugs need to be sized together so that the link lifts the barrel just enough for the lugs to slide into a tight lock up on the stop. If the link is longer than that it will just egg out in 5,000 - 10,000 rounds returning everything to the kind of sloppy lock-up you're seeing. Neither your lugs , nor link show any sign of the expected "shine" where they fit each other correctly. If it were my gun, I'd measure my barrel top lug engagement and on that basis make the decision between a shorter link, or an oversize stop. Probably the stop as your stop also seems sloppy in the link currently. If you are capable of taking accurate enough measurements, I would also buy a +od/-ID bushing from EGW and and fit that at the same time. This is pretty well understood work, having been performed on hundreds of thousands of well used surplus 1911s over the years. It's the kind of "tightening up" I'd expect to be needed on a pistol with 80,000+ rounds down the tube where the slide lugs and barrel top lugs have worn past sufficient lock-up engagement, the slide stop holes in the frame are worn a little large, the lower link hole is worn a little large, and the slide stop cross pin is grooved a tiny bit from the barrel lugs and stop. Rattles when you shake it? Standard fix would be a .200 slide stop with a .005 taller link and a new fitted bushing. While in your case it looks more like sloppy fit from the factory, I think the fix would be the same. If you do this work, don't be surprised if it shoots a bit differently to the sights. Shorter link will raise POI a bit, oversize stop and longer link will lower POI a bit.