"All .45 acp cases headspace on the case mouth. It does not matter if it is a wheelgun or a semi-auto. SAAMI specs determine this. Now some moonclips might hold the cases without them actually touching the chamber shoulder, but that is irrelavant.(Seems real relevant to me) ALL rimless (not .22s) semi-auto handgun cases headspace on the case mouth."
The Colt 1917 I owned at one time did not know that. A loaded cartridge would drop straight through the cylinder. My Star Super B in 9mm Largo don't know that either. It headspaces 9 mm P on the extractor and functions as well with those as with 9 mm Largo. I have stopped doing that because it's hard on the extractor and those are very difficult to find these days.
Btw, you fearless experimenters can make high strength .45 ACP cases by cutting any of the .30-06 family of cases to length. I'd use milsurp .308 for cost. You are on your own for data because the case capacity is smaller..