My boy calls these guns the Hammers.
I have two M81s and two M8s, essentially identical except for cosmetics. The M8s are both in .30 Rem, while the M81s are in .300 Savage. The M8s are tolerable to shoot, but the M81s are unpleasant to fire with full power .300 Savage loads. For that reason, I make up lighter .300 Savage loads for them. Ammunition is not a problem, as it is fairly simple to form .30 Rem brass from .30-30 cases, if you have a lathe (which I do) to machine the rim off and cut a new extractor groove. Takes about two minutes per case to do. They can be reloaded using .30-30 dies. It is a snap to make .300 Savage cases from .308 Win brass. Just FL size in .300 S die and shorten the neck.
I believe that. The recoil of mine in .35 Rem is terrible.
My .300 Savage reloads normally use gas check cast bullets, and loaded just enough to function reliably. Cases usually land a few feet to the right so I don't have to hunt for them. My load is 23 grains of IMR 4227 with a 170 grain cast bullet. My favorite is a Grade 2 M81 with peep sight on the rear of he receiver. Shoots very good groups at 50 yards. I would like to have one of the special police/FBI rifles with extended magazine capacity.I had an 81 in .300 Savage. Shot well even with cast bullets. However, about every third or fourth empty would land square in the middle of my forehead. You didn't want to fire that gun without wearing a snugged down cap or hat.
My smallish Southern Ohio hometown police department had a Thompson in its armory that was bought back in the 30s just in case one of the notorious motorized bandits of that era showed up to terrorize the town. I saw and handled it once, but long ago. Probably no longer there today.