That post got me to thinking about some of the guns I've shot over the years, and certainly this was one of the most novel:
I noticed a man at the local range firing an unusual single action. From my viewpoint, the gun looked brand new, and when I got the chance, I asked him about it. He very grasciously allowed me to examine it, and offered to let me fire it.
This gun was an original Colt 1860 Army Model converted to cartridge via the Richards-Mason conversion. The barrel had been cut to five inches (or so, shortened very expertly). The gun had been re-blued, maybe several times, and the backstrap was silver plated. The grips were obviously the original walnut, and showed considerable wear. Now these conversions were in .44 Colt, right? The rounds he had were .45 ACP, with maybe a 155 gr. or 173 gr. SWC bullets, very conical. He told me they were loaded with a black powder substitute.
The gun felt like a mild .38 Special when firing, and accuracy was terrible, but .45 ACP it was. The owner told me he had inherited the gun from his father-in-law and he knew nothing else about how it got to be shortened or how it became a .45 ACP.
This was such a handsome gun and it sort of flung a cravin' on me for one of the replicas, which so far, I've been able to resist.