Colt had been making their NEW SERVICE model revolver for the Brits and Canadians in .455 for several years when the US entered WW1 in April 1917. Immediate massive US Army requirement for all military firearms, and Colt helped by getting about 150,000 made by the end of January(?) 1919, chambered for the .45ACP cartridge. S&W produced a similar number in .45ACP on their large frame Hand Ejector 2nd Model, which they also had been selling to the Brits and Canadians in .455.
The Colt New Service in .45ACP had a "war-time" finish and was cranked out as fast as the factory could. There should be military marks and serial number on the bottom of the grip-frame and a lanyard ring. If you can still find them, you can chamber and safely use the .45 Auto Rim cartridge, specifically introduced in the early 1920s for this and the S&W wartime made revolvers.
This particular Colt model had a decent single action pull, but requires a strong handed man with extensive training to do any decent double action shooting. Watch your right thumb when shooting, as the cylinder release latch is quite angular in shape and will draw the blood of the careless on recoil. Substitute the rounded last version of this latch if you intend this piece mainly as a shooter. Rifling is quite shallow for the metal cased bullet, and I would suspect that lead bullet accuracy would be problematical.
It's a very standard revolver, and the usual 2nd-hand inspection techniques will apply.
Above all from the RAM in my hair-topped computer, so all comments are "IIRC".
