Is it possible to have a Sub-Machine gun like an Uzi in something larger than .45acp? Or does it become an Assualt Rifle once you get into Larger Calibers.
I haven't been by "Full Auto" to see if you asked, there.
Anyhow, "sub-machine gun" is a class of full-auto critter which uses pistol cartridges. SFAIK, .45ACP is as big as any of them get. Remember, "caliber" refers to bullet size, not overall cartridge size.
Anybody else chimes in, I'll move it to FullAuto...