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The Yugoslavian M56 looks on the surface like it's derived from the German MP40, and the form factor is much the same, that's what they were looking for, but it's different in a lot of ways. Mechanically, it's a bit closer to the Italian Beretta subguns of the era.
While lacking the MP40's nicely contained recoil spring assembly, and not having quite as nice ergonomics, the M56 has a particularly long receiver, in which the bolt itself never actually reaches to impact the back of it, instead slowing down until the spring shoves it forward again. This 'constant-recoil' setup, comparable to guns like the Swedish m/45b, makes the recoil impulse extremely gentle, and this gun is very easy to control in full-auto as a result. It also uses a magazine with a two-position feed, unlike the MP40's single position feed magazines, so they're similar to the Russian PPS-43 subgun's, but not interchangeable, and holding 32rds instead of 35rds.
There's some quirks to the design, the stock is almost a little bit short, the pistol-grip is kind of square feeling, and if you want to grip the gun out on the front like the MP40, it gets a little bit hot (but the magazine is also not as delicate or flimsy so it tolerates that better), however you'll do just fine using the handguard behind the magwell. The ejection port is also on the top, rather than the side, and it ejects pretty much straight up into the air, thus you'll get those 7.62mm Tokarev casings coming back down on you, which doesn't hurt, but it can be distracting if you're not used to it.
It's possible to not quite fully assemble it all the way after disassembly, leading to a situation where the receiver could pop open during shooting, which would be very dangerous, but as long as you mind to do it correctly, it's fine. At some point they found that the plastic lower could crack in particularly harsh cold, and the fix for this was to bolt in a little block of wood inside of it (I don't know why this worked, but it did).