Does a 1911 Chamber have a taper?

[warmrain]

In troubleshooting some handloads I discovered that one of the two Kimber Ultra CDPs that I own (two years apart) has a smaller chamber dimension than the other. The Kimber with the larger chamber seems to be closer to my Colt Officers in dimension. The only reason I could tell was that some hand loaded rounds failed in the one Kimber (FTrB). A drop test into the chamber showed that one Kimber was smaller than both the other Kimber and the Officers...

Where this is going...

Today with some rudimentaty "inside" dimension tools I attempted to measure the chamber dimension of the "smaller" Kimber and the Colt Officers for comparison. The tools were not precise enough to make a determination, but in both cases it seems that the chambers actually have a small taper...

Sanity check: is it so? :confused:

[Hunter]

The 1911 chamber should not taper but could be slightly if the reamer was dull or out of spec. A go no go headspace gauge would tell you for sure if you had a tapered chamber. The chamber should be .898" for good headspace and .920" as excessive headspace

[warmrain]

Thanks Hunter, though I'm not looking now at headspace but at diameter...

[Hunter]

What I meant was if the slide would not close on the .898" go gauge it might not mean that it is a short chamber but the chamber has a slight taper not allowing the gauge to bottom out on the end of the chamber where the case mouth headspaces the round. If the go gauge will not allow the slide to close it is either a short chamber or a tapered one. Sorry about not being clear.

[warmrain]

Ah! I get it now. Good point!

[1911Tuner]

No. A correctly spec-ed .45 ACP chamber shouldn't be tapered. However...I've been running into more than my share of tapered chambers even in high-end match barrels over the past three years. It's one of the first things that I check whenever I run into a sluggish return to battery when all else checks out as "Good to Go" in feed reliability. I rarely drop a finishing reamer into a new chamber these days without coming out with chips. This happens too often for me to chalk it up to occasional dull tooling. It almost has to be intentional...and I believe that it's done to wring out every last drop of accuracy from whatever barrel is used. The problem is that it gives very little accuracy increase...if any at all...in return for reduced chambering reliability. Testing has shown that the accuracy differrence between the stock chamber dimensions and the finish-reamed dimensions on the same barrels...fired with known accurate ammo from a solid rest...amounts to less than 1/10th inch for an average of 5 groups at a distance of 25 yards.

[Hunter]

Would the thinking behind a tapered chamber yielding more accuracy be that the round will index better centered to the barrel than a non tapered chamber? I was wondering what logic was being used in intentionally tapering chambers.

[1911Tuner]

Dunno bud, unless it's a result of the manufacturers cavin' in to the public demands for match-grade accuracy from a fighting pistol...as if 4 inch(sandbagged) groups at 50 yards ain't good enough. :rolleyes:

I know that I've solved a good many feed/return to battery issues on many pistols in 5 minutes with a finishing reamer.

[Pappy]

I measured the I.D. of my Eclipse chamber: At front 0.472" and at the rear 0.479". a 0.007" taper...Pappy

[Pappy]

Just dug up my copy of Roy F. Dunlaps "Gunsmithing" 1959 edition.
It has a chamber drawing showing .4879" at the rear and .4723" at front. So looks like a taper has been around for a while...Pappy

[1911Tuner]

Just dug up my copy of Roy F. Dunlaps "Gunsmithing" 1959 edition.
It has a chamber drawing showing .4879" at the rear and .4723" at front. So looks like a taper has been around for a while...Pappy


That doesn't sound right, Pappy...Lemme check my specs and get back to ya.
Several "gunsmithing" books have been a bit wide of the mark, with some dimensions taken from an example gun rather than blueprint specs.

Be back later...

[1911Tuner]

Basic Ordnance spec allows for .0045 inch maximum taper taken from breechface line to stop shoulder to be within spec. Likely to allow for varying case head dimensions. The taper that I've encountered has been more on the lines of .015 inch, with the miked diameter at the stop shoulder in the neighborhood of .468-.470 inch. My finishing reamers hold that to less than .002 inch,
with the shoulder diameter running to about .477 or so.

[Pappy]

Johnny, I would think that a slight taper is more desireable than a true cylinder if only to aid in extraction. Yes??
P.S. Did you get my PM??

[1911Tuner]

Johnny, I would think that a slight taper is more desireable than a true cylinder if only to aid in extraction. Yes??
P.S. Did you get my PM??

With a high-pressure round like the 9mm...yes. With near black-powder peak pressures such as the .45 ACP, not necessary. Didn't get a PM...it should be along soon, but it's XXXX Nix the part about Vic Mackey...Dang pain meds lied to me about waht night it is. it's Monday...Medium night!

ciao

[warmrain]

Pappy,

These are just about the same dimensions I'm finding though I'm using an inside caliper and then trying to mic those... So it's not good for an absolute, but the taper is definately there, in both Kimbers Ultra CDPs and the Colt Officers too...

I find it insteresting that my reloading manuals are calling for a 0.473" taper and that the chamber dimensions both measured in your Eclipse and quoted from the Dunlap are 0.472" (or there abouts). That might explain why my 0.473" (spec.) hand loaded crimps were occ. not going into battery. Now that I've tweaked them down to < 0.472" they are reliable...

[Pappy]

The US army wanted a new pistol to stand up and be effective for wartime conditions. I'll bet the original specs called for a tapered chamber to aid extraction. (along with varying case head dimensions). Mud, sand and dust getting on ammo and fouling up the chamber would cause extraction difficulties if the chamber were truly cylindrical.
Anybody have access to the circa 1911 blueprints???
Very interesting...Pappy

[1911Tuner]

Taper is variable due to tooling wear and or machine spindle runout variation. Navy armorer's prints call for the diameter at the stop shoulder not under .475 inch. Just for the record...If a pistol destined for serious purpose comes across my bench with that dimension tighter than .475 and taper exceeding .010 inch....it gets a finishing reamer right of the bat.

A 1911 pistol that's timed within specs, and fired with true GI ball or close equivalent will run pretty well without an extractor at all...and a pistol
that does that puts very little stress on the extractor, assuming that proper magazines are used.

The "New/Improved" blueprint specs may indeed call for more chamber taper than original specs allowed in order to aid extraction with some of the hot-rod, double-throwdown +p stuff that seems to be the trend these days. So...you may be correct in that light...but it wasn't always so.

[Pappy]

Just for the record...If a pistol destined for serious purpose comes across my bench with that dimension tighter than .475 and taper exceeding .010 inch....it gets a finishing reamer right of the bat.



Johnny, just out of curiousity, does your finishing reamer have a taper??
Thanks...Pappy

[1911Tuner]

Johnny, just out of curiousity, does your finishing reamer have a taper??
Thanks...Pappy

Yep. .003 inch

[warmrain]

Johnny, Is that .03 inch designed or is it due to wear...?

[1911Tuner]

Johnny, Is that .03 inch designed or is it due to wear...?

Design. All the finishing reamers that I've used had about .003-.004 inch of taper per inch. May be due to variations/tolerances during the manufacturing.

[John]

Excuse me, but I have to assume that we are talking about .45 ACP barrels, right? I mean, aren't the 9mm barrels tapered, since the cartridge case is tapered as well?

[niemi24s]

FWIW:

The Springfield Armory blueprint dated 10 Aug 42 (available on this site) for the USGI M1911A1 barrel, shows the chamber stop shoulder diameter of 0.474 +0.002 inches, and a chamber taper specification of ".008 Inc. T.P.I. Basic". The "Inc" is for "Included", indicating it includes both sides of the taper, so the figure given relates to the diameter, not the radius - which would be for just one side of the taper.

An article in the April 1963 American Riflemen by Capt. Carl J. Davis, USA, "The 1963 National Match .45 Pistol", confirms this earlier taper specification and gives a chamber taper specification for the (then) new National Match "414" barrel of ".004 Included Taper Per Inch Basic". The 414 is the last three digits in the part number for this barrel, which is NM7791414. [This article is a treasure chest of information. I miss the good old days when the Rifleman had articles with technical merit!]

The Lyman Cast Bullet Handbook shows the 45ACP case with a .473" diameter mouth and a diameter just forward of the extraction groove of .476. As the case length listed is the .898 maximum, the two diameters may also be maximum diameters.

IMHO, the M1911A1 chamber is tapered cuz the 45ACP case is tapered - not much, but still tapered - at a bit less than 0.003" included per inch.

[Lazarus]

So, do the prints specify a taper because the .45 round is slightly crimped during loading, or are the chambers tapered to insure that most rounds headspace properly on the mouth of the case?

As far as the accuracy approach is concerned, Wil Schuemann has introduced the "AET" barrel with a fluted chamber. The flutes are supposed to insure that the round "self-centers" during firing, by allowing the expanding gases to slither around the case. I don't imagine the accuracy improvement is really worth all the extra fouling that is bound to happen. But, I haven't personally tried such a barrel.

-Lazarus

[John]

Here is a piece of the blueprints:

http://img.photobucket.com/albums/v323/sv1cec/posts_pictures/chamber.jpg

I am not sure if I can read them correctly, so you more experienced machinists can decide.

[Spindly61]

I'll give it a shot:
.474 dia. + .002 with a concentricity of .002 in relation to "A"(ball seat diameter). TPI must mean taper per inch,
I'm used to that meaning threads per inch but we all know it isn't threaded.
The check mark with a 32 above it refers to what is called a "Surace Finish"". This means very shiny and flat.We are getting deep when it gets into surface finish and microns, I don't want to bore you.
Everything else is pretty basic. Some of the refrences are on the print elsewhere.Any questions ask. I've been out of the trade for awhile so bear with me.

[Spindly61]

I broke out my machinist handbook(Boy did the type get smaller)
TPF= Taper per foot. TPF= 12(D1 - D2) divided by length
TPI= Taper per inch TPI= D1 - D2 divided by length

[1911Tuner]

The taper is to help with reliable extraction in a minimum-spec chamber...but doesn't do a thing for reliable chambering and return to battery when such a chamber gets fouled. Going on what I've seen in recent years, the match chambers are at or near minimum, and the taper is over the edge...too much.
Helps with accuracy...a little...but not enough to make the problems that it causes worth it except maybe in a precisely-built and extremely accurate gamer...and even then it can get tiresome. The taper isn't an issue when the chamber is mid-spec or larger...but can be a real headache in minimum chambers. A quick pass with a finishing reamer...hand-turned...usually cures'em.

Recall the extraction issues with the M-16? It was largely because the chambers were tight...they were too straight-walled...extractor too small, and the case rims too thin. Go to the AK47 with its loose dimensions, sharply tapered case, thick rim, and heavy extractor.

[niemi24s]

I've no idea why the chamber IS tapered, except that the maximum specs for the loaded cartridge allow for a tapered case. Note that this does NOT mean that a particular loaded cartridge will (or must) have a taper. The only factory loaded stuff I have on hand is Western Super Match with a 185gn jacketed semiwadcutter and when measured to the nearest 0.0001", the case shows essentialy no taper at all. A round of Federal Ball had an included taper of about 0.002" per inch.

Factory jacketed ammo doesn't appear to be crimped at all, and the bullet is held quite securely by the friction between it and the case. Handloaded with cast lead bullets, the case is usually (but not always) given some sort of crimp. If crimped, the resulting reduction in case diameter occurs close to the case mouth, and doesn't affect the cases's overall taper - if it had any to start with. Because of all this stuff, I think it's safe to say the chamber is NOT tapered to accomodate any cartridge with a crimped case mouth.

None of my blather, of course, answers the "Why IS it tapered?" question. Maybe they're just a whole lot easier to make with a slight taper and they end up with a better surface finish. Maybe the fundamental question is "Why do the maximum loaded case diameter specifications describe a tapered case?"

I make a motion we close this thread before somebody gets a square electron stuck in their microprocessor. All in favor . . . . . . . .