This is a cursed AF gun kitbash. Stock looks like a Mauser, trigger group looks like a PPSH, rear sight looks like a Garand, magazine looks like a G43, and the muzzle birdcage looks like an M14. It also took me ages to realize that suppressor-looking thingy is supposed to be on the side, because even with the barrel sticking out it really looks like that's where the action feeds into.

Best guess re: the weapon request is that this is supposed to be something from Valkyria Chronicles, but honestly the only tag I can apply is bad gun anatomy.