The semi-automatic Reising Model 60 .45 ACP, shown (top) with a 12-round-capacity magazine, was intended for civilian plant guards and other security personnel. The Reising .45 ACP Model 50 Submachine Gun, shown below with a 20-round-capacity magazine, was adopted by the Marine Corps in early 1942. Photo courtesy of Smith Photographic Services, Shreveport, La.
USMC Reising Model 60 carbine
The M60 was a long-barreled, semi-automatic carbine model designed primarily for military training and police use. However, few of these were ever sold. The Marines used M60s for training, guard duty, and other non-combat roles. Some M60s were believed to have been issued to Marine officers at Guadalcanal.[9] The remaining guns were passed on to State Guards and civilian law enforcement agencies. The M65 was developed as a sub-caliber training rifle version of the M60, produced only from 1944 to 1946. H&R later made updates to the M65 and sold them on the civilian market (and to the Marines in small numbers) as the MC-58 and M150/151/165 Leatherneck.[10][11]
Top: Military Model 50 Reising, Center: Model 55 Reising, Bottom: Commercial Model 50 Reising
I think a 12 round semi auto 45ACP M60 would be a funny SA Rifle low damage but balanced for a 5 round BA rifle. The 6 Round M55 without stock could be fun as a ‘sidearm’. yes silly but they did exist and while not used as such where used and or tested by the army. It could give some badly needed variety to low BR without threatening power creep.