Consider a .458 American 2"

https://en.wikipedia.org/wiki/.458%C3%972-inch_American

Brass can be made from any standard belted magnum



Edit: reread the original post -- short action -- so -- Bushmaster


Edit again: There is also the .45 Raptor that is essentially a rimless .460 S&W. You would not have to worry about getting a rebated rim cartridge to feed and eject properly.

Last edited by dSmith_45; 01/19/21.