I just watched a few videos about the israelian TAR21 rifle which is literally the real life counterpart to the TRG21 in ArmA3 and one thing that I noticed was that on the real TAR21 the charging handle doesn't move while firing while the TRG21's in ArmA 3 does move.
It's a real minor issue but I think it's worth getting fixed simply because it adds a little bit of unrealism to the game.