i think that reformism and .45 boomerism come from the same strain of thought. yeah no shit recoil is hard to control with full power cartridge (like AR-10 in .308 that he has), that's why intermediate cartridge was developed. this gets worse in handguns
Depends where in Europe, in a lot of countries it's quite common (although not anywhere near the amount of the US), it's just that the culture is so different that most Europeans don't flaunt them or see them as a part of their identity like Americans do
Edit: I originally just automatically (ha) assumed you meant all autoloading weapons, but upon further thinking I now realize that you probably meant fully automatic guns. In which case I don't think those are really a thing outside of like Czechia/Slovakia, but I'm not actually so sure