I didn't make it!
I was wondering why I couldn't hit the broadside of a barn with an MG34 in certain situations, so I did some testing on a LAN server without bots or other players.
Shooting at a wall I noticed that the bullet impacts where always offset to the left of the ironsight, yet the ironsight is perfectly centered on the middle of the screen. I've also made the experience that, if you are prone and shooting past an object (a barrel, a wall, whatever), you will frequently hit the object and thus supress yourself, but only if you are to the right side of the object.
I've found the root of the problem: If you watch the targetting animation (switching to iron sight), you may notice that it isn't a straight zoom. The field of vision wanders a bit to the right, in order to line up the iron sights of the MG34. There lies the problem. The "real" invisible muzzle of the weapon doesn't follow the movement of the field of view in the targetting animation. Hence the shots are offset to the left of the ironsight.
Solution: You'll probably need a new targetting animation with a straight zoom. I myself see no concrete alternative, but I'm not that an experienced modder, I admit.