Doll's heads, by their shape, can only prevent the action from pulling straight back off the barrels, or the barrels from moving straight ahead off the action face. The barrel lugs and hinge pin prevent this movement from happening. A doll's head will not even start to prevent a double's action from coming off face. It can't, as it's shape allows the barrels to move in exactly the direction it is suppose to stop. I can se no benefit with a doll's head. I suppose it can correct sloppy lugs from allowing the barrels to swing left and right when in the locked positon, - probably why they're on Belgium guns.[;)]