I agree. The current aiming system is crap. Once in a while, if you crouch you can see down the back sights, but then sometimes the gun isn't mounted so you can see down it when you crouch, and either way if you angle the gun up or down at all then you can't see down the sights any more.
The animations are pretty goofy too, just standing still behind it, having it move around on its own (telekinesis maybe?). Not to mention being able to turn 180 and shoot through your back.
I think the system for using mounted weapons needs to be reworked. When a player uses a mounted weapon, his player model should grab onto the weapon and move with it when angling it. From the first person perspective, the player should automatically keep his view down the sights, and turning the weapon 180 from where it's mounted, or straight up into the air, should be disabled unless it's mounted that way to begin with. As it is now, the M2HB is more like an unfinished easter egg novelty than a weapon properly implemented in Inf.