
Hey Everybody

Allow me to toss in a comment or two. First: for Buckaroo Lou - The ACP cylinders are indeed machined to seat on the case mouth of the ACP cartridge. This also holds the cartridge rim proud of the cylinder breach, allowing a Cowboy 45 Special case to be loaded and seat on the case rim and have correct head space. Works a treat.
ALL - I don't know what brought up the Auto Rim, but that cartridgege is an entirely different kettle of fish. The Auto Rim doesn't fit in anything not spatially machined of the AR cartridge.
The end dimension of the C45S and the ACP cartridge, from the rim forward are identical. This allows the the two cartridges to be used in an ACP cylinder interchangeably. The benefit of the C45S design, was to provide far less internal volume for reduced loads to be able to compete with the 38special shooters. A side benefit of the ACP chamber can be elimination of the "jump" from case mouth to throat of the 45 Colt chamber. The jump can effect accuracy although I have found no difference in accuracy between 45 Colt chambers and 45 ACP chambers. As a reduced load BP cartridge, the C45S is SUPERB.
Lets Have Fun Our There
PS: I one had a swell pair of USFA "DOUBLE EAGLES" to which I fit Uberti 45 ACP cylinders, just for C45S cartridges. Wish I had kept them now.