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Will 45 Auto Rim work in a Colt/Ruger SA revolver?


Chief Rick

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Title asks the question.

45 Auto Rim, rim thickness = 0.0827 in (2.10 mm), rim diameter = 0.5154 in (13.09 mm)

45 Colt, rim thickness = .060 in (1.5 mm), rim diameter = .512 in (13.0 mm)

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From an NRA  publication:

 

Q. Can you safely shoot a .45 Auto Rim cartridge in a revolver chambered for a .45 Colt? A buddy of mine gave me some the cartridges, but I don’t have a gun in .45 Auto Rim. I do have a .45 Colt, though, and it looks like it should work.

A. I would not encourage anyone to attempt to fire a .45 Auto Rim cartridge in a cylinder chambered for .45 Colt. Aside from differences in the dimensions of the cartridge case, the Auto Rim round has a significantly thicker rim, approximately 0.090" versus approximately 0.060". This could certainly cause headspace and functioning problems. If the revolver in question is supplied with a separate cylinder specifically for the Auto Rim cartridge, there should be no problem. A number of firearm manufacturers have over the years offered .45 revolvers with dual cylinders, one for .45 Auto Rim or .45 ACP cartridges and one for .45 Colt.

-Reid Coffield

Originally published September, 2006

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43 minutes ago, Sedalia Dave said:

The issue is going to be headspace. There will not be enough room for the thicker rim to have sufficient clearance to allow the cylinder to rotate. 

That's what I was thinking but I didn't/don't have the means to verify and I don't want to waste money on brass that I would otherwise have no use for.

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If you want short brass that will be guaranteed to fit in .45 Colt guns, then get Cowboy .45 Special brass.  Or do as I do, and trim tattered .45 Colt cases to the 0.898" length that the C45S is made to. 

 

good luck, GJ

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4 hours ago, Garrison Joe, SASS #60708 said:

If you want short brass that will be guaranteed to fit in .45 Colt guns, then get Cowboy .45 Special brass.  Or do as I do, and trim tattered .45 Colt cases to the 0.898" length that the C45S is made to. 

 

good luck, GJ

I have C45S and also trim 45 Colt already.

 

I've never seen a 45 Auto Rim case in the wild and was wondering.

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Long before the C45S was invented, I would thin the rim of .45AR cases so they'd fit in a single action. I'd use a piece of a bolt inserted into the case to keep from crushing it, chuck it in a lathe, and thin the rim from the front side so as to not reduce the depth of the primer pocket. Another method was to cut down the older style balloon head cases, but they've become quite scarce over the past few decades. Cutting down modern .45 Colt cases is often hit or miss - below the "neck", the case walls get progressively thicker and the expander plug and seated bullet bulge the case, sometimes to the point they won't chamber easily, or at all, depending on the case and/or bullet.

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Howdy

 

Left to right in this photo: 45 Colt, 45 Schofield, 45 Cowboy Special, 45 Auto Rim, 45 ACP.  The 45 Colt, 45 Schofield, and 45 Cowboy Special all have rims .060 thick. The 45 Auto Rim has a rim .090 thick.

 

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45 Auto Rim was developed as an alternative to shooting 45 ACP with half moon clips in the Colt and Smith and Wesson Model 1917 revolvers. Here is a Smith Model 1917. There is more space behind the cylinder to allow for the half moon clips. With 45 ACP loaded onto half moon clips the cartridges headspace on the clips. Without the clips, 45 ACP can be shot in the S&W Model 1917, because the rounds will headspace on the case mouth. But the extractor will be useless because there are no rims for it to grab. The clips allow the empties to be extracted. A stick will work to pop the empties out of the Smith, but not too good in a combat situation. I don't own a Colt Model 1917, but I understand that without the clips, a 45 ACP round will not headspace on the case mouth.

 

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Anyway, that is why the 45 Auto Rim cartridge was developed, the thicker rim allows it to take up the extra space behind the cylinder, and the extractor can engage the rims to eject the rounds.

 

A conventional 45 Colt revolver does not have enough space behind the cylinder to accommodate the thicker rims of 45 Auto Rim.

 

However..........there's always a however isn't there, some revolvers have the rear of the cylinder specially relieved to allow for clips or thick rims. At least I think so.

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@Driftwood Johnson, SASS #38283 the early Colts were bored all the way through, but it was quickly changed so that the .45 ACP rounds would headspace if no moon clips were available. The S&Ws were cut to headspace from the beginning.

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