45 Auto Rim brass

[Battis]

I have a M1917 S&W .45 revolver. It can shoot .45 ACP ammo with or without moon clips. Now, the .45 ACP cartridges without moon clips headspace on the case mouth. With the moon clips, do they headspace on the rim (moon clip) or still on the case mouth?
The reason I ask is that I read that you can't use .45 Colt brass because the rim isn't as thick as the rim on the .45 Auto Rim, but would that really matter if they still headspace on the case mouth?
I'm not trying to reinvent that round, and I have .45 AR brass coming, but I'm curious. I do have some .45 Colt brass. Again, just curious.

[Wayne Dobbs]

On the rim, like the other rimmed cases do...

[Battis]

So take it one step further - if I used 45 Colt cases, where the rim is not as thick as the 45 AR, would there be headspace issues if the cartridge still headspaced on the case mouth? In that scenario, the case would headspace on the case mouth and the rim would be large enough for extraction.

[TenTea]

Trying to chamber a cartridge ~1.6" into a revolver chambered for a cartridge ~1.25" may be an exercise in futility...moon clips or not.

YMMV

[Char-Gar]

You ask an interesting question. 45 Cowboy Special cases are nothing more than 45 ACP cases drawn on the 45 Colt head. The original purpose was to enable Cowboy Action shooters to shoot reduced loads of black powder in their 45 Colt revolvers. It did just that, but accuracy is lousy, because of the long jump the bullet has to take in the cylinder before it engages the cylinder throat. Gilt edge accuracy is not needed in that sport, so everybody was happy.

The 45 Cowboy Special however, is a crackerjack case for the 45 ACP cylinder in various single action revolvers. Unless modified these cylinders can't use 45 Auto Rim cases due to the lack of headspace room between the case head and the recoil shield. The chambers in SA 45 ACP cylinders are a smidge shorter to enable the naked ACP case to had proper headspace.

Now to answer your question, I took some loaded 45 Cowboy Special rounds on my desk and tried them in my Smith and Wesson 1955 Target Model (45 ACP). These rounds fit the ACP cylinder just fine, but the headspace was far more than I think is acceptable or perhaps safe. I am not certain the firing pin would reach far enough to give good ignition and if it did, those cases would come rocketing back and smack the recoil shield of the revolver pretty darn hard. Harder than I would want.

Bottom Line: Using the thinner 45 Colt case rim in a Smith and Wesson DA revolvers would created an unacceptable headspace problem. This is why the 45 Auto Rim case rims are so darn thick.

Of course trying to use full length 45 Colt cases would be a non-starter, because you could not close the cylinder by a very long way.

[Harter66]

I would presume that your Colts cases would be cut/trimmed to correct ACP head space length ?
If so when I tried it it didn't go well . That was in a Colts 1917 when I run across those 12 cases again I will try them in the S&W cylinders and the ACP cylinder for the BlackHawk
I can't remember exactly what the problem was but I do remember that they dragged badly on the frame face.

[Battis]

I should have added that I'd cut the .45 Colt to length.
If the distance from the primer to the case mouth was the same as on a regular .45 ACP, I'd think the firing pin would hit the primer as it should.
If the .45 ACP case was too short, or crimped too much, it might not headspace properly, just as a thinner rim in a .45 AR might affect the headspace.
Interesting. Thanks.

[Harter66]

I haven't tried it but the modern Colts may have a sufficient groove above the rim to allow for a moon clip or a tight fitted spacer on the ejector . A peened moon clip cut to say 90° around the case under the rim and spot peened to stay firmly attached to the ejector center but be removed without tools .

Lots of thought , a few doodles , no models ......

[Der Gebirgsjager]

The earliest production 1917s did not have the step in the cylinder chambers and were bored straight through with the same diameter. This was because they were designed from the beginning to use the half-moon clips, and the designers didn't foresee the problem that would result if they were fired without the clips. The result was that the firing pin drove the case farther into the cylinder and if the cartridge did fire it was difficult to remove it. So the cylinders were redesigned to have the step, and .45 ACP can still be fired in them without the clip but something like a pencil is required to punch them out, usually not difficult. As observed by Char-Gar, a .45 Colt trimmed to length might fire if the firing pin was long enough to span the space that would normally be taken up by the clip's presence, but an unfavorable recoil situation might exist. You just can't go wrong using the Auto Rim cases, if available. You might also wonder about the older M-1908 revolvers, outwardly identical to the M-1917s, that were chambered for .45 Colt. Firing a .45 ACP in one of those gives the same result as firing a .45 ACP in a 1917 that lacks the chamber shoulder.

[Char-Gar]

I suspect the confusion is a result not taking into consideration there are really two types of "headspace" in this puzzle.

First there is case headspace. The 45 ACP case headspaces on the case mouth and the AR case and cut 45 Colt case headspace on the rim. This case headspace holds the round in place so the firing pin can strike it.

Second there is dynamic headspace, which is the distance between the case head and the recoil shield of the revolvers frame. This dynamic headspace must be short enough for the firing pin to strike hard enough for good ignition. Even with ACP cases or AR cases in S&W or Colt DA revolvers, the hammer nose has a long throw. Folks who try and lighted the mainsprings on these revolvers soon find out they get bad ignition or no ignition at all, due to the lighter hammer nose strike.

Now put a shortened 45 Colt case in said revolver and you double the dynamic headspace placing the primer farther away from the hammer nose strike and allowing the fired case to come back hard against the recoil shield with greater force due to the increased space between the case head and the revolver recoil shield. Restated, the thinner rim of the 45 Colt case creates way to much dynamic headspace.

If you are the kind of guy, who simply can't understand that fire burns without sticking your hand in it then, cut some 45 Colt cases and have at it. If will only take a few rounds to break the code for your self. The confusion will roll away after a round or two, if they fire at all. What you will have done is create excessive dynamic headspace.

[TenTea]

Thank goodness for an answer steeped in eloquence rather than my *square peg / round hole* answer to the OP.

[Harter66]

If the case hits on the mouth and the head is where it's supposed to be what difference does the rim make ?

If a belted magnum headspaces on the shoulder .0005 off the belt headspace with the bolt closing freely on the now over length cartridge is it a headspace risk ?

If the dynamic headspace is the same or shorter than the clipped ACP and/or the AR and/or ACP without a clip (no headspace device except the case mouth) then the thin rim is a moot point just as the belt is on a mag where the shoulder hits be fore the belt . This in no way suggested mouth headspacing a 450 Marlin in 458 Winchester brass cut short but that does draw a more descriptive picture .

[Battis]

If you are the kind of guy, who simply can't understand that fire burns without sticking your hand in it
Now there is an overused response...

I thought it was a good question, and I still do. Riddle me this - why is there not excessive dynamic headspace when a .45 ACP round is fired in the stepped chamber with no rim or moon clip?
Other than being used for extraction purposes, how does a thinned rim effect headspace? What if a .45 ACP case had a small thin rim - would the headspace change?

[Der Gebirgsjager]

The difference is that the half-moon clip itself provides some thickness and resistance to the fall of the firing pin. It also lends itself to ready extraction. If there is a step/shoulder in the cylinder the round will fire, but you'll need to punch out the empties. The Auto Rims though will usually extract like any rimmed cartridge by using the ejector rod.

[Char-Gar]

Now there is an overused response...

I thought it was a good question, and I still do. Riddle me this - why is there not excessive dynamic headspace when a .45 ACP round is fired in the stepped chamber with no rim or moon clip?
Other than being used for extraction purposes, how does a thinned rim effect headspace? What if a .45 ACP case had a small thin rim - would the headspace change?

You obviously did not read my posts or didn't try and digest the information contained therein. As a reloader and revolver shooter of 55 years, I will take my leave of this thread. My counsel to you will be don't try and get creative with reloading until you understand the basics of revolver mechanics.

[Battis]

don't try and get creative with reloading until you understand the basics of revolver mechanics.
Another overused response.
All that I asked, and it's pretty simple if broken down, is whether or not the rim on a 45 AR case, and/or the moon clip used on a 45 ACP case, changes the location of the headspace. I think that's a pretty advanced question, beyond the knowledge of basic revolver mechanics. And what does 55 years of reloading have to do with it unless you have reloaded that particular round for 55 years?

The best answer I got was, "If the case hits on the mouth and the head is where it's supposed to be what difference does the rim make?"
Which makes me think that a 45 Colt case, cut to length (of course), that has a thinner rim than a 45 AR, might still headspace on the case mouth AND provide a rim for extraction only, as would a moon clip made from "space age hydrocarbon polymers." (EZ Moon Clips)

Am I going to try it? No. As I said, I was just curious.

[Dale53]

I am going to ignore that little voice in my head that says "Stay out of this"...

There are a couple of things that were NOT discussed above.

1 - Modern S&W revolvers should NOT be fired with .45 ACP cases without clips (S&W changed the headspace protocol). The new revolvers do not necessarily headspace on the mouth of the case. This has been discussed in some length in Handloader by Brian Pearce (with important comments from Tommy Campbell a factory pro). It is no longer practical to shoot .45 ACP's without clips in the newer Model 625's and 25's. As a "real world" example, I have two 625's - one will work without clips and one will not (they changed the ball seat and they no longer provide support for the case mouth). So, that alone would rule out using cut down .45 Colt cases for me.

2 - The second issue is that without sectioning a number of .45 Colt cases, I don't know if the solid base of the cases would provide support for the base of the case (it won't necessarily be the same as .45 ACP cases and .45 Auto Rim cases). An unsupported case could, in theory, blow out the side of the case (just as some .45 ACP cases have in unsupported chambers from various .45 ACP autoloaders over the years).

As a matter of interest, I ordered out five hundred .45 Cowboy Special brass for another project several years ago. When I got my Ruger Bisley .45 ACP/.45 Colt convertible, I tried those cases in the .45 ACP cylinder and they headspaced perfectly and worked really well when using heavy bullets that had a crimp groove - I could use a roll crimp as the case headspaces properly on the case rim.

.45 Cowboy Special cases are not always easy to find and they are expensive. So, shortened .45 Colt cases would work well in the Ruger Bisley with the .45 ACP cylinder (they would, in effect, be the same as the .45 Cowboy Special).

Just a thought or two...

FWIW
Dale53

[Char-Gar]

I am going to ignore that little voice in my head that says "Stay out of this"...

There are a couple of things that were NOT discussed above.

1 - Modern S&W revolvers should NOT be fired with .45 ACP cases without clips (S&W changed the headspace protocol). The new revolvers do not necessarily headspace on the mouth of the case. This has been discussed in some length in Handloader by Brian Pearce (with important comments from Tommy Campbell a factory pro). It is no longer practical to shoot .45 ACP's without clips in the newer Model 625's and 25's. As a "real world" example, I have two 625's - one will work without clips and one will not (they changed the ball seat and they no longer provide support for the case mouth). So, that alone would rule out using cut down .45 Colt cases for me.

2 - The second issue is that without sectioning a number of .45 Colt cases, I don't know if the solid base of the cases would provide support for the base of the case (it won't necessarily be the same as .45 ACP cases and .45 Auto Rim cases). An unsupported case could, in theory, blow out the side of the case (just as some .45 ACP cases have in unsupported chambers from various .45 ACP autoloaders over the years).

As a matter of interest, I ordered out five hundred .45 Cowboy Special brass for another project several years ago. When I got my Ruger Bisley .45 ACP/.45 Colt convertible, I tried those cases in the .45 ACP cylinder and they headspaced perfectly and worked really well when using heavy bullets that had a crimp groove - I could use a roll crimp as the case headspaces properly on the case rim.

.45 Cowboy Special cases are not always easy to find and they are expensive. So, shortened .45 Colt cases would work well in the Ruger Bisley with the .45 ACP cylinder (they would, in effect, be the same as the .45 Cowboy Special).

Just a thought or two...

FWIW
Dale53

Dale....Just a couple of reponses to your excellent post. When they first came out in 1989, I bought a 5" 625 in 45 ACP. These were put together for a newer shooting game that required a fast drop in reload of ammo in full moon clips. The rear of the throat was tapered that made the use of ammo without clips iffy at best.

Your issue of blow out heads on 45 Colt cases was on my mind as well. The thin rims of the Colt case really increase the distance between the recoil shield and the case head. If the case head was forward in the cylinder, I doubt the hammer blow would set if off. If it was toward the rear to much of the web would be exposed with the possibility of a blow out. Newton's 3rd. Law tell me that the cases would shoot back against the recoil shield hitting with force beyond the design specs and exposing more of the case head that makes me comfortable.

I too have had good luck with 45 Cowboy cases in ACP cylinder in SA revolvers. They allow me to roll crimp the Keith SWC bullets in the crimp groove and have the round headspace on the rim.

[Der Gebirgsjager]

This information is welcome, and all good-to-know stuff. I also have two 625s in the 4" Mountain Gun configuration in .45 ACP, but honestly the thought has never occurred to me to try them with anything other than full moon clips. But just a slight tug back to the original subject, it was about 1917 model revolvers, or so I thought.

[17nut]

The 45 Auto Rim came out as a replacement for 45 ACP in clips, thus the way thicker rim.
Mainly for the Colt 1917's and shaved Webleys.

How did the 45 Cowboy Special come into play here?
A shortned 45 LC with a rim that is to thin for proper fit.

https://www.starlinebrass.com/brass-cases/45-Auto-Rim-Brass/

The .45 Auto Rim has an extra thick rim that allows it to be used without a moon clip in revolvers designed for .45 Auto/moon clip combination. It is built with the same integrity as our 45 Colt case.

[Char-Gar]

This information is welcome, and all good-to-know stuff. I also have two 625s in the 4" Mountain Gun configuration in .45 ACP, but honestly the thought has never occurred to me to try them with anything other than full moon clips. But just a slight tug back to the original subject, it was about 1917 model revolvers, or so I thought.

It was indeed, but the issues of using cut off 45 Colt cases remains the same. If anything the issues are worse in a 100 year old revolvers with a century of use and century old metallurgy.

[Tackleberry41]

The cut down 45 colt would fit, yes. But doubtful it would fire, there would be a large gap between the back of the case and the firing pin. The ACP and the moon clip is the same thickness as the auto rim, rim. But thicker than a 45 colt.

I have cut down 45 colt and 454 casull cases to fit in a 45 acp conversion cyl in my blackhawk. You cant roll crimp an ACP case to prevent recoil from pulling the bullets out under 460 rowland recoil. I did try some 45 AR cases, just out of curiosity, not they wont fit, rim is to thick. AR is to thick for a blackhawk, 45 colt is to thin for the old S&W.

I bought a bag of the AR cases, not horribly expensive. And work with a speed loader. I have a pile of full moon clips, but wanted the AR cases just to have them.

[Harter66]

There is .0227 difference in the AR and Colts rim . The Schofield shares the rim thickness of the Colts but is slightly larger dia .

The Colts neck dia is .480 vs the ACP at .473 SAMMI . So the Colts is larger dia going in plus our cast bullets up to .458 vs spec of .451-2 .

If we bide by the light taper , no , just enough crimp to remove the flair AND we have a proper 45 ACP chamber then at least for the purpose of headspace this should be a non-issue .
If a revolver cylinder will accommodate a moonclip and/or any rimmed case and the Colts , Schofield , 454 , 460 or Savage , 308 , Mauser or 06' families trimmed to .898 then again it shouldn't be an issue because the larger diameter case with the same sized bullet is head spacing on the mouth NOT on the rim .

The difference in thickness of the AR and Colts family rims is .0227 inches unless I missed something and my Winchester , Starline , Rem or AP brass doesn't have the tapered web I think it does I don't believe it will thin enough fast enough to be a significant threat to case failure . We're looking at Colts with a working max at 14,000 psi and ACP at 21,000 psi where Ruger only loads run up to 25,000 without​ case failures .

Someone mentioned loading Rowland levels ......why...... Anyway with virtually unlimited seating length it's a non-issue to burn a little more powder and keep the pressure down . Most ACP cylinders are way longer than the max OAL of an ACP .

This brings us to function . Making the presumption that we have a cylinder that correctly headspaces on the mouth of an unclipped ACP . The Colts do wander and the cylinder doesn't move freely the first pass when the bottom half of the case is sized small the 2nd go is better but I would still consider it a stop gap not a fix .

My next project is to Schofield an APC revolver I have invested a great deal of time in this exploration .

[Battis]

If you measure the length of a 45 ACP case (a case that headspaces on the case mouth) and cut a 45 Colt case to the exact same length (and size it), basically you're making up for the thinner rim of the 45 Colt case with the case mouth. The case will headspace on the mouth, and the rim will be used for nothing but extraction. The distance from the firing pin to the primer will be the same. It's basically a 45 ACP case with a rim. I primed a few cases that I made and they worked fine. I also posted the same question on the Smith & Wesson forum and apparently it's not a new idea, it's safe, and it works fine with loaded ammo. Some posters wondered why I'd ruin perfectly good 45 Colt brass when 45 AR brass is readily available. I have some 45 Colt brass that I don't need so I figured I'd try it.

[Harter66]

I had some with mouth splits .