A lot of antique cartridge brass is a bit different than original spec now. Most have a bit of extractor groove that the original form didn't have, and the rim/head area is a bit different since they're not balloon head brass anymore.
45 Colt headspaces on the rim, nothing forward of it. Those grooves in the cylinder may be for headspacing 45ACP using clips, if what you're describing is what I'm picturing as a little lip in each chamber.
Last edited by zcm82; 11/24/21.