Home Forums Reloading Handgun Reloading 45 acp and auto rim

Since the same revolvers handle both is there a reason 45acp load data can't be used in 45 auto rim?

Smaller internal case capacity?

In 1917, Colt released the M1917 revolver chambered in 45 ACP. As the 45 ACP was a rimless cartridge, the revolvers required the use of moon or half-moon clips to facilitate extraction and proper headspacing. These revolvers were issued to US troops in World War I to supplement the distribution of the M1911.

Although the half-moon clips were effective, they were easy to lose or misplace. If this were to happen, there are two potential issues. The first is failure to extract. Without a rim to hold onto, the extraction arm has nothing to grip and therefore rounds would have to be ejected from the cylinder one at a time with a field expedient object (think pencil). The second issue would be headspace. As the 45 ACP has no rim for headspace, it’s possible that a round could slip into the chamber and fail to fire.

To fix these issues, the Peters Cartridge Company developed the 45 Auto Rim in 1920. This new round was nothing more than a 45 ACP with a rim.

The new ammo allowed for the rounds to be fired and ejected without the use of a moon clip. 45 Auto Rim is compatible in revolvers chambered in 45 ACP, however it should not be used in a semi-automatic 45 ACP pistol.

I've used 45 ACP data in 45 AR cases. It works fine until you get to top-end loads. From there, you have to proceed on a gun-by-gun basis, just as you do every time you get to top-end loads.


Okie John

seems that commonly published data shows the acp is loaded to higher pressure. i'm wondering why.

Powder capacity is the same.

The NRA Handloading Guide says:

"The maximum average chamber pressure for the .45 Auto Rim is established at 16,900 c.u.p. This is less by 3,000 c.u.p. that the limit imposed on the .45 ACP, which should emphasize the advisability of loading conservatively for the old Model 1917 revolvers."

The #13 Speer Manual says the max is 15,000 c.u.p.

I use same data for both. Not plus +p by any means but middle of road loads

No.

okie john is correct.

The NRA Handloading Guide is telling you to load an Auto Rim (in so many words), to a lower level than the cartridge the 1917 WAS actually chambered for?
The real reason is that it (the 45AR) was factory loaded with lead bullets and they generally hit the same speeds as the 45 ACP did with less pressure. They also reduced barrel wear.

The 1917's might be old but they certainly aren't weak unless they've been neglected or damaged or not correctly repaired.

Another thing, 45 Auto headspace shoulders were cut into Colt 1917's, Smith 1917's, 1950 Targets, 25's, 26's up until the 1990's. The simultaneous ejection was the major hiccup in 45 ACP revolvers. Firing them was generally not, except in perhaps very early guns.

Until Starline started making Auto Rims, the case was generally prone to cracking because it was pretty thin towards the case mouth.

Complete guide to handloading by Sharpe, my copy 1937 makes absolutely no difference in loads for ACP or AR in the only powders still around, Unique & Bullseye. Amazing how the people including Hatcher were all wrong.

Were there any +p .45 ACP loads listed in 1937?

i understand, but weren't the moon clips designed to permit the acp to be used in those same revolvers?

The 1917 revolvers were a wartime expedient to use Colt's and S&W's current manufacturing capabilities to produce handguns quickly.

I assume the NRA publication's recommendation reflects 60 years of experience shooting full power ,45 ACP loads in these old revolvers? Just as some of Elmer Keith's 44 Special loads are now understood to be a bit much.

i get that but i'm not interested in elmer level loads, just the "standard" 45acp level loads especially in modern revolvers.

I would have zero concerns about shooting "standard" .45 ACP level loads, loaded in .45AR brass in a modern revolver.

They'll be fine. That's what they were made for.

Even plus P out of a perfectly fine working 1917 in good condition, especially the Colt 1917.

Heck, for that matter I would be comfy in shooting hotter loads in a Colt New Service than a copycat 1911 of dubious background. Those revolvers were hell for stout, within their genre, and I've seen some 1911 clones that would've been better off in the landfill. Back in my younger/impetuous days I hotrodded a few New Service revolvers (1920's vintage .45 Colt and .38-40, and a .45ACP 1917 to a lesser degree) with some hellacious loads and none of them whimpered. The .38-40 in particular got special treatment: 180 cast bullet + 8, sometimes 9 grains Unique, and sometimes I tiptoed over that line. Never a stuck case or any other signs of over-stress but I quickly backed off to 8gr. loads because frankly I was scaring myself. +P is ok, but +P+ in a vintage Colt is a sobering experience if one has a modicum of common sense.

Note however that Colt (and S&W) upped their metallurgy game in the 1920-1922 time period resulting in a much better safety margin over the WWI 1917 models. If I were to resume shooting a Colt 1917 I think I would hold up with standard pressure hardball loads as a maximum. As it is I'm quite happy anymore putzing around with mild semi-wadcutter loads in my Gold Cup, and occasional hardball sessions with another Colt 1911.

thank you all for your insights and expertise.
as i said, i'm not truing to use +p loads or emulate elmer kieth. i simply trying to understand that published 45 acp loads would be reasonable in the 45 auto rim. i still don't get why the auto rim wasn't loaded to the same level as the acp from early on.

It was

Julian Hatcher states in one of his books that the 45 acp and 45 AR were both loaded to 230 grain @ 835 fps for the military.

Phillip B. Sharpe states in his 1937 book once again that the factory load for the military in 45 ACP and 45 AR were identical 230 grain @ 835.

History of Colt Revolvers for the 1917 states that the AR round was identical to the 45 ACP except for the rim which was incorporated to get rid of the S&W half moon clips.

Good info here. I load the 255 gr Keith SWC to 45 ACP pressures in my 25-2.

https://www.handloadermagazine.com/45-auto-rim-p