I think it helps a little bit. Without it, I’d stop shooting when I saw the enemy go behind something in order to preserve ammo. With it on, I tend to continue shooting and get the kill. I use it with the Barret .50 and a couple other rifles. You need to get the 40 penetrating kills (a kill behind a wall, door, etc…) to get the extended mags, which gives you the gun mastery achievement which is 10,000XP. It definitely comes in handy when you need 50-60,000XP to go up one level.