You can shoot .45 ACP and Auto Rim out of the same gun, but not .45 ACP and .45 Colt. Two cartridges of the same "family" - .38 Spl/.357, .44 Spl/Mag, as noted above - are OK, but you can't mix cartridges. No .45 GAP and .45 ACP, for instance. I bought some HKS "slow loaders", to see if I wanted to give ESR a whirl with my 22-4, and it looks like a real pain, especially compared to just dropping-in a moon; the pin in the center of the 'loader hits the pin in the back of the cylinder before the bullets have entered the chambers, so unlike the sort of self-aligning moonclip, some care is required to make sure the 'loader is properly aligned with the cylinder or the rounds aren't going to drop in.