I'm afraid you misunderstand what I suggested for the SGA. With a magazine of 20, a typical heavy ammo pickup in the Crucible would give a player 30 rounds or so, and maximum capacity would be around 60. Suppose you shot at a player 12 times and hit him 4 of those times. You would lose 8 rounds total, because the 4 that connected would return, leaving you with 12 rounds left in the magazine.