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Old May 11, 2012, 05:01 PM   #47
Jim Watson
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Join Date: October 25, 2001
Location: Alabama
Posts: 18,483
Quote:
The auto rim is basically a .45 ACP with a rim. It was designed to be used in in revolvers that require half moon clips.
And the rim is very thick, about .090" instead of the usual .060" so as to take up the same headspace as ACPs in clips. It is not interchangeable with anything else I know of, and is not usable in single actions with ACP cylinders.

Note, there is a thing called the .45 Cowboy which is the length of an ACP with the rim of an LC. Made for real tenderfoot loads. No problem in a revolver but a lever action .45 Colt rifle has to be gunsmithed to handle the much shorter round.

Historical note, in 1906 Frankford Arsenal produced a .45 Revolver round the same as .45 Auto except with a standard rim. I don't know if anybody offered up a revolver to shoot it in the Army trials. The 1909 New Service stopgrap revolver was chambered .45 Colt and the Army loaded special large rim diameter shells for it to give better simultaneous extraction. I don't know why it didn't get the short FA cartridge.
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