a rifle that originally started as a drawing i made a while back
Yeah get rid of the handle and rebuild it so that it has I would say less than 100 faces. Also instead of making the barrel so incredible dense you should have started with a cylinder that has less than 24 verts.
Over-all you should be aiming at less than 1,000 verts if you really want this in a game. Even 1,000 is probably too dense for a game.
At 61,000 faces this isn't even close to low poly, and without textures or UV mapping this model would be completely unusable in a game.