I just posted all of this over at the High Road, so I am pasting it in here.
Left to right in this photo the cartridges are 45 Colt, 45 Schofield, 45 Cowboy Special, 45 Auto Rim, and 45 ACP. Not immediately obvious in this photo, but the 45 Schofield rim is larger in diameter than the 45 Colt or 45 CS rim. SAMMI standard for the 45 Colt rim diameter is .512. That is the same rim diameter as the 45 CS. However, because the 45 Schofield round was designed to be extracted by the extractor star of the Schofield revolver, the rim diameter for the Schofield round is .520.
How about the short round with a .45 Colt rim? That’s the .45 S&W, which is sometimes called the .45 Schofield or-infrequently-the .45 Short Colt. Built to equal the original performance of the .45 Colt in the shorter-cylindered Schofield revolvers, this cartridge was dormant for decades. The SASS people brought it back to life for their modern shooting sport. I would have bet that this would be the solution, but I was wrong. It turns out the .45 Schofield is a perfect fit in length for what we are seeking, but the rim is shaped to be incompatible with some of the guns guys are using in the Cowboy shoots.
There are two inaccuracies in this statement. The 45 Schofield cartridge did not equal the performance of the 45 Colt cartridge. It couldn't. The reason S&W developed the Schofield cartridge was their tooling was set up for cylinders 1 7/16" long. They were in the midst of the Russian contracts, and the 44 Russian cartridge only needed a cylinder 1 7/16" long. When S&W bid on a contract to supply the Army with revolvers, competing with Colt, the Army specified that the revolvers must be 45 caliber. Opening up the chambers and the bores from 44 to 45 was no big problem, but the 45 Colt cartridge was too long to fit into a 1 7/16" cylinder. Rather than change their tooling in the middle of the lucrative Russian contract, S&W proposed an alternative cartridge, not too long to fit into a 1 7/16" cylinder. The 45 Schofield cartridge was the result. Black Powder cartridges are stuffed completely full of powder, unlike Smokeless cartridges there is never any empty airspace. The relative size of a Black Powder cartridge is a reasonably accurate comparison of how powerful it is. The 45 Colt originally held 40 grains of Black Powder under a 250 grain bullet. This was later reduced to 30 grains in the cartridges supplied to the military, with cardboard wadding taking up the empty space. The charge in the 45 Schofield cartridge was about 28 grains of Black Powder under a 235 grain bullet. Clearly, not as powerful as the original 45 Colt design, and slightly less powerful than the military 45 colt cartridge.
Regarding the rim being incompatible with revolvers used in CAS, again, not true. In almost every case, the extra diameter of the 45 Schofield cartridge does not prevent it seating properly in a 45 Colt revolver. Trust me on this, I have shot Schofield rounds in Colts, Ubertis, and an original Schofield. The only case I am aware of, is an 'original model' Vaquero of mine. One chamber, and one chamber only, does not have quite enough clearance for a 45 Schofield cartridge to seat completely. About five minutes with a file took care of that.
Regarding the 45 Cowboy Special, it is not a new round. It first appeared probably close to ten years ago. It was the brainchild of a Cowboy shooter, and as has been stated, the idea behind it was to make for a more efficient round when loaded lightly than the 45 Colt. When loaded lightly with Smokeless powder, the large volume of empty airspace in the 45 Colt can make ignition spotty and the burn can be inefficient. Reducing the extra air volume in the case makes for a much more efficient burn. Anyway, the inventor of the round contracted with a brass manufacturer, I do not know who, to produce a production run of the brass, and he was the exclusive seller of the brass. After a while, because of health problems he got out of the brass business, selling the rights to make the brass to another shooter. Then there followed a few years when for several reasons the brass was hard to come by and very expensive. Finally, Starline started producing the brass, I have to guess they bought the rights to it from the latest owner. That is why we are now seeing the 45 Cowboy Special brass being marketed by Starline.
And by the way, the 45 Cowboy Special round is much too short to function properly in a lever rifle. One can modify, or buy, a modified carrier for a toggle link rifle (1860 Henry, 1866 Winchester or 1873 Winchester) that will allow the 45CS to cycle properly in a lever gun chambered for 45 Colt. Otherwise, the round is much too short to feed properly in a lever gun. I am not aware of any modifications that will allow the 45CS to function properly in a Winchester Model 1892. I'm sure if somebody really wanted to, the 1892 carrier could be modified to work with the 45CS, but I am not aware of anybody who has done so. As it is, converting a toggle link rifle to feed 45CS is pretty rare.
Regarding shooting the 45 Auto Rim in revolvers instead of 45 ACP with clips, count me as one. There was quite a long thread about this quite recently. I prefer to shoot 45 Auto Rims in my Model 1917 Smiths, I don't want to mess around stuffing rounds onto clips. By the way, the 1917 S&W revolver will fire a 45 ACP without moon clips just fine, the rounds headspace on the chamber throat, but you need a stick to poke out the empties.
