After posting on a previous thread that straight wall cases shrink, not grow, as they are used, which I think is wisdom we have all received from “authoritative” “experts”. I decided to do a bit of measuring in my brass pile.

Conclusions; It is evident that these .45 acp cases have not “grown”. Whether trimming would in any way help taper crimped cases is debatable. I think they are stable at this point and probably reached stability after one or two cycles.

Measuring.
My pile probably is not as large as many, but just may have some older brass. My Uncle started shooting .45 acp in the 1920s while in the National Guard, he continued well into the 60s when he gave me his 45 reloading “stuff” which included a lot of older military brass.
It is true that I do not know how many times this brass has been reloaded. I know that some say they are able to tell from extractor/ejector marks on the case, this method is a fail for me. My Uncle and I kept all of it in circulation for a number of years until two years ago when I decided it was time for some old veterans to retire. Since then when I inspect, I pull out old mil cases. I do not try to keep track of the number of times I have reloaded handgun brass except for some max loads of 44 Magnum. As a rough approximation I would say the pile turns over every two to three years.
It’s also true that I don’t know how long any of the cases were when manufactured.

The oldest case is FA 4 15, that is from the last qtr of 1915, next is FA 35, (I think I have some FA 34 but where? maybe loaded?), WCC & FA; 43 & 43 several, then examples from every 5 yrs or so after. So I have some representative cases varying from 95 years old to current.
I have weighed many of the cases and I do not see significant variations. I full length sized all before measuring, the typical case is mouth is not square by .002-.003”.

Case length specification (max)for.45 acp is; .898”
The actual measurements of this many times fired brass falls between .888 and .897”. A very peaky histogram with most from .889-.893, with a few outliers at .888 and .894-97”. I checked 20-WCC 43 ave = .8908”
And now for the strange part the longest cases I have are the 15, 35, and two of the 41s, the 15 is .897” and about .002” out of square.
I checked some Speer once fired cases they run .891-.894” I trimmed to square the mouths and ended up with ..889-.892”.
So the old and older brass ends up about the same length as the new once fired cases.

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Ipsis Rebus Dictantitbus

+100. This exactly mirrors my experience.

I once got into quite a "discussion" about how it was impossible, because the 45 headspaces on the case mouth. The other fellow just couldn't believe me, but it is true. In fact, the 45 (and most other auto pistols) headspace on the extractor.

Oh, and one other thing - On the few pieces of new brass I've gotten. After sizing, it's no longer than the multiple-fired brass I have in 45ACP. I don't think the brass shrinks. It's shorter than "trim-to length" to begin with, and because it's such a mild-pressure cartridge, it never gets to the stretching stage...

I guess you disagree with the manufacturers of both guns and ammunition who design their products to headspace on the case mouth for .45 ACP, .380 ACP, 9 mm, .40 S&W, and 10 mm. Just ask S&W, Glock, Ruger, Speer etc. and they'll tell you. It makes no sense to have a critical dimension like headspace depend on the asymmetric tiny contact area between the extractor face and the cartridge rim.

I used to shoot a couple thousand rounds of .45 ACP a month and never noticed that the brass ever grew. It always got thin and cracked before any thing else happened. I now shoot lots of .45-70. Some brass that I bought new a few years ago was 2.084 to 2.087 instead of 2.10. After nearly 10 years of use and bunches of reloading (the primer pockets are getting loose), it has finally stretched to 2.10 - 2.105. Never had the stuff shrink but it grows pretty slowly.

Yep.......

I have seen very impressive arguments about just how a 1911 headspaces on the 1911 forums. Some very opinionated people who all seem to know where-of-they-speak hold very different views on the matter.

Mechanically I don’t see how a pistol can headspace on different length cases if there is much variation. You will note that the specifications do not give a minimum only a max. I do know that a case which is too long will not let the pistol go into battery. But short cases shoot just fine.
Clearly the extractor does hold the case head against the slide. Now if the case is short where is the rim in the barrel?
There is no compensation built into the design which lets it lock up differently on a short case. Does the short case headspace on the rim and is not then held against the slide by the extractor?
Granted we are talking about a few thousandths still how does it work?

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Ipsis Rebus Dictantitbus

"I guess you disagree with the manufacturers of both guns and ammunition who design their products to headspace on the case mouth for .45 ACP, .380 ACP, 9 mm, .40 S&W, and 10 mm. Just ask S&W, Glock, Ruger, Speer etc. and they'll tell you. It makes no sense to have a critical dimension like headspace depend on the asymmetric tiny contact area between the extractor face and the cartridge rim."

In theory, yes. In practice, not so much.

If you have the tools, measure the depth of your .45 ACP chambers to where the "headspacing" shoulder is. Then, measure all of your .45 ACP brass. I doubt you will find any that are long enough to actually headspace properly on the case mouth.

While you have the barrel out of the gun, drop a bunch of that brass into it and see how deep it goes, which translates to how short of actually hitting the case mouth on that shoulder they often are when the gun is assembled.

Yep, the extractor holds the brass against the breech face.

Any experienced .45 ACP gunsmith can confirm this for you.

I have never found a .45 ACP cartridge case grow to the maximum length, either. Never had to trim one.

Case length on the .40 is supposed to be .850. I have measured some of the "premium" grade ammo and they will run pretty near that, or more often, a tad less...maybe .848-.849. The "white box grade" varies widely with some being as short as .842, yet all feed, fire and extract normally, poor headspace notwithstanding. So, even if they do stretch slightly they are getting closer to what would be the correct length. I typically use starting loads for practice. The pressure level of these is in the vicinity of 22,000 CUP with the components I use, which is in the range of a .45 ACP +P. Pretty mild for a .40 and about 20-30K rounds later I see no reason to red line them.

I certainly would not recommend the practice, but one of our firearms instructors routinely fired .40's in his Glock 10mm, hundreds of them in my presence. The extractor held the case against the breech face tightly enough for the gun to function normally.

And, that kids (please don't try this at home) is how I convinced myself of the truth of the matter. (I previously held the same opinion that the factories knew what they were doing and were not filling us with propoganda...) Having done it once, I won't get into a drawn-out pi$$ing match over the issue again. If you don't believe me (us), it's America; you're entitled to your opinion...

I would suggest an experiment for doubters. Trim some cases. My shortest is .888’ trim off another .010” the pistol will not know the difference.

I had a 1911 in for tuning and a barrel. When it came back it would not fire factory loads, only some reloads, and not all of them. Turned out that the chamber was reamed a bit short so that the pistol would not go into battery with cases close to max.
I have checked barrels, not easy because the rim is not much to measure to, but about .905” seems to be max. That being the case and your experience may vary, almost none of my ammunition is head spacing on the case rim.

I don't think the factories have any evil intent, after all what difference does it make. The basic design has worked for more than a 100 years. It’s just that the details are often more complex than we think.

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Ipsis Rebus Dictantitbus

I have accidentally tested the case being held back by the extractor when sometimes pesky .380 cases somehow crawled over into the 9mm Luger brass. Not only did the Dillon load the cases without complaint, the Paraord fed and fired them normally. Only way I knew what happened was when I found the split .380 case lying in my pile of fired 9mm on the ground. A properly adjusted extractor covers a multitude of sins in case length.

Hello, While I am not a gunsmith, nor do I play one on TV etc., I am a Colt O-Frame armorer and have owned, used and worked on quite a few 1911 type pistols since 1965. I humbly and respectfully disagree with those that believe the O-frame, or any other pistol that I'm aware of, headspaces on the extractor. With the .45 ACP, no-go headspace is .920", minimum is .898". Yes, the case can be a Lot shorter than .898" and the pistol will still function normally. The firing pin can and will drive the cartridge case forward and still ignite the primer with a case Much shorter than .898". If you will field strip your pistol, slide a .45ACP case of any length into position beneath the extractor, pull the case forward and you'll see that the case is free to move forward .050" or so depending on the individual tolerances of your particular gun,extractor,etc. So, unless your barrel's headspacing shoulder is Grossly out of spec and/or the case is Grossly shorter than spec, your gun is not headspacing on the extractor. Knowing this, Pachmayr custom 1911 type guns, years ago, had a spring-loaded plunger in the breech face to push the case forward into firm and consistent contact with the barrel's headspacing shoulder. You can take the extractor completely out, or have the hook break completely off, and the cartridge will still fire. With GROSSLY excessive headspce, cartridge cases may blow out over the unsupported area over the feed ramp, split or display pierced or severely flatened primers. I have measured the actual headspce on about 35 .45 ACP handguns over a period of quite a few years. The tightest I have ever found is .900" (on a S&W performance center pistol ) and the loosest was .921" on two Colts that I had purchased new. The average of all the guns measured was .912". Although I much prefer tighter tolerances, all fired and functioned normally. Due to it's relatively low operating pressure, the ACP tolerates, what I consider quite a bit of excessive headspace, with no ill effects. In fact, headspce that is slightly over .920" will not generally cause any problem with factory ammo or quality reloads IMHO.

It has been my experince that upon firing, straight-walled pistol cases do get shorter, as they expand radially, and will lengthen several thousands upon full-length resizing. I never trim straight-walled pistol cases, as I have rarely ever found a straight-walled pistol case at, or even very close to, max case length. ymmv

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NRA Life, COTEP 640

I never trim new brass to the "trim to" length, because I know that the cases will shrink with usage and go below that length. I trim to a few thousandths above the trim to length, to try and uniform the brass as best I can.

I don't know the answer to the extractor vs. case mouth headspace debate, but this is a great discussion. Thanks to everybody with something positive to add.

I built a few 1911s in the '80s in .45 ACP and one in .41 AE, and never built one that headspaced off the extractor. The fact that a firearm will fire that way is a testament to its design, but it is malfunctioning and will eventually break if not attended to.

It also doesn't headspace off the rim, the rim is for extraction.

oldRoger, out of curiosity, what did the brass you measured measure before they were fired? Without that information the rest doesn't really mean anything.

This came up in the prior discussion too. There's only two problems with it:

One, if you have grossly exagerated headspace, like the 40S&W in the 10mm Auto chamber, and your firing pin can still reach that far forward (which it can't on a Glock due to the design of the striker and breechface - and I'm a Glock Armorer, btw), then you're going to get headspace-type problems. Most-noticably, the case will expand at the body and grip the chamber walls, and then unsupported and unexpanded base portion of the case will still flow backwards until it hits against the breechface, and this will result in case-stretching and eventual weakening of the web. And, we've already determined this is NOT happening, because the cases do NOT stretch...

Second, you'd have to have one very long and loose extractor to allow the case to move forward that far in the chamber. (A 40S&W in a 10mm chamber, for example.) I know from experience with my 1911s (most-all military WWII vintage) that the extractor can be fairly loose, and the firing pin protrusion of a 1911 can be enormous, but that's only on that pistol design. And, even then, if this was happening, we'd have cases stretching, which clearly they are not...

Now, the 380 Auto is a straight-walled case and the 9mm is tapered (as is it's chamber), so theoretically, the mouth of a 380 case may engage the tapered 9mm chamber at a point far enough to the rear to provide headspace. Honestly, I haven't checked the dimensions to see if that's true. But when dealing with a straight-walled case, the extractor does it.

As another example I can give, we had an officer once who picked up a bag of 40S&W ammo and loaded it into his 45ACP handgun. He fired three rounds before the gun locked up on him. There was definite headspace-connected issues with that third round (the gun had to be hammered open), but the first two rounds fed, fired, and ejected just fine (albeit with horrible accuracy and massively split and expanded cases). My hypothesis, is that the first two rounds headspaced on the extractor and worked fine, but the third round (with the 40S&W rim dia. being so much less than a 45's) escaped the extractor, or possibly popped out from around the extractor due to the firing pin strike, and that resulted in the headspace problem on that one.

Lastly, as a final alternative, there are those who continue to load the 45ACP with a roll crimp. Even though all the load manuals say not to, they got a set of dies (back in the old days) which had a roll-crimp-type die, and they adjusted it just like their revolver dies, and they haven't had any issues for thousands of rounds... How can that be, if they're supposed to be headspacing on the case mouth?

Yes, the engineers and designers are not purposefully putting out propganda, but the fact is, sometimes stuff in the real world doesn't work like the engineers and designers intended, thought, or SAY they would.

The amount of tolerance that is built into the system (between the min & max chamber cut lengths and the min and max brass lengths, there can be quite a variation) means that the extractor was probably designed as the primary headspace system with the case mouth being the back-up system. This way, when the gun is working as it should (loading from the magazine), the extractor always slides over the front of the case rim into the extractor groove.

The case mouth/chamber headspace shoulder is there as a back-up so that if someone drops a round into the chamber and then hits the slide stop to slam the slide down on the round, the extractor (which has a cam ground on it's front surface and spring-tension to allow it to pivot around the rim and snap over) has something to stop the cartridge so that this extractor-grabbing action can happen. (Otherwise, the face of the extractor would just shove the cartridge deeper.) THIS is why I think the factories and engineers want that headspace shoulder. If it wasn't there, there's nothing for the loaded round to resist-against to stop it, so that the pressure of the slide slamming forward can force the extractor to snap around the rim.

Now, this is just my opinion, but, if I am right, here again, we have another example of John Browning thinking out ALL the possibilities and designing for them, so that any minimally-trained GI will have a functional weapon, even if he's not operating it exactly right.

Jellybean; I don’t know how long they were. I am going to pull a couple of factory loads just for the heck of it to check but since no one that I know pulls measures and reloads new factory rounds and then finds, reloads and measures at each step, this question will remain unanswered, especially in regard to the 1915 & 1935 brass. I have never had any new unfired .45 brass.
It really makes no difference. The question was; “do we need to trim to length”? The answer is that even the very old and much fired brass in my sample does not grow (stretch might be a better term) to exceed the Max. specified.

As regards the head space controversy, it’s probably a semantic question. When the round is chambered it is normally held (loosely) by the extractor, and most generally the case rim does not touch the step in the chamber.
So we field strip as Rock185 suggests and put the barrel in battery. It is locked in place and the tolerances are what they are. If we have too long a case it will not allow us to lock up. If we have to short a case it is not tightly held anywhere. As Rock185 points out there is tolerance in the extractor, which allows movement between the case head and the slide. There is also tolerance between the rim and barrel.
So a long firing pin hits the primer pushing it forward. This is not a hard push, nor a very long one, only until the primer detonates (.010”?). There is some slight further forward pull as the bullet leaves the case. Then the case is pushed hard against the slide. Does the case rim contact the barrel as the round travels forward? I suggest that in some cases, perhaps many, it does not we know that from the .40/10mm example. Does it make any difference?

What we seem to have is a round which is not really held tightly against the breach or against the barrel step in most cases.
Most auto-loading pistol rounds are designed to headspace on the rim. Do they??

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Ipsis Rebus Dictantitbus

It sounds like we're comparing apples to oranges here. Proper Headspace versus whether an extractor will hold the rim sufficiently enough to allow the gun to fire. Because it can doesn't mean it should.

All good points. I think it is correct to assume that Browning intended the shoulder and extractor to each be able to achieve a functional fit (for lack of a better term), depending on the conditions at hand.

In illustrating the various types of headspace, Hatcher relates how he fired many .45 ACP's in the Webley & Scott .455 Self-loading pistol and .380's in the Luger or P-38. Again, if they could be fed from the magazine and thereby secured by the extractor, fit of the cartridge against the breech face was adequate to fire them.

oldRoger, the rim does not engage the barrel in a 1911 and there is no shoulder for the rim to touch. The cartridge is supposed to headspace on the case mouth and there is a step in the barrel for the mouth to sit against. The back of the cartridge then sits flush with the barrel hood which protrudes from the top back of the barrel. In battery the hood sits firmly against the slide and the cartridge isn't dependant on the extractor at all at that time. If you take a S&W model 1917, or other .45ACP revolver, you use moonclips for extraction because the case is "rimless". You can still chamber and fire the ACP ammo without the moonclips and it will work fine except you will not be able to extract them with the revolvers extractor. The use of the term 'headspacing on the extractor' is incorrect as no cartridge is designed to do this. The only time the case is held in place only by the extractor is if there is a malfunction or other problem like excessivly short ammo.

Some auto rounds do headspace on the casemouth and some are semi-rimmed such as the .38 Super and are supposed to headspace on the little bit of rim that is available. Even then, some .38 Supers are made to headspace on the case mouth because it is more reliable then headspacing on their tiny little rims. Even though many firearms will fire with nothing but the extractor holding the case in place, I have never seen any that were designed that way. Not saying they don't exist, but I've never seen one.

I pulled bullets from three factory rounds and then full length sized the cases and measured, 2 were 893”, 1 was 894” this is a bit more than most of my old fired brass.

Jellybean; I know how a 1911 is supposed to work. The step in the barrel left by the chamber reamer is the “shoulder” I was referring to above, I had a mind spasm and couldn’t think of the right word. In this discussion I should say case mouth and barrel step, but didn’t always do so.

If you look at what Kuhnhausen has to say and his illustrations about barrel fitting , ramping, and chambers, he is clearly talking about what happens when the round is not pushed forward until the case mouth hits the step. See above for what mma10mm, rock185, and cjw3 say about what is happening inside.
Kuhnhausen says headspace should be checked with a headspace “go” gauge in place, headspace then is the “go” gauge (.898”) plus what ever additional feeler gauge the barrel will close over. The Max is .920” which is the no-go gauge size. This check is best done with the extractor out. Since the barrel should be locking on the first locking lug, a measurement from the barrel extension to the step will only approximate the headspace.
While most match barrel headspaces are .898” + .010” or slightly less, Mil Spec Pistols are up to the .022” allowed.

Dead center of the headspace tolerance is .909”. Since we know the brass is likely to be around .890” We would have .019” of space either at the case mouth or between the case head and the slide or split between them.
Worse case is a max spec headspace and short brass, then we have .030” of slop.
The crux of the argument is whether the round is pushed into the chamber by the slide, if so the case mouth probably will not be at the barrel step. If it does get to the step there is nothing to keep it there.

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Ipsis Rebus Dictantitbus

oldRoger, rock185 is correct and he's not agreeing with you or the other posters. Headspace is misunderstood by a lot of shooters and it appears as though that is the problem here.