I disagree on the gut wrencher mod. I play on PC. At the beginning of the game, I had a controller connected to my PC and I used it to play FC6 among other games. The MOMENT I switched to playing with a mouse and keyboard, I started landing headshots left and right, and all guns became a 1 hit kill, provided that I don't miss, of course. Even if you're not very good at headshots, use burst fire mode and aim at the upper chest area. The recoil should make the second or third bullet hit the head. Also saves ammo as opposed to auto mode. So if your aim is good enough, I recommend a different mod, such as an extended mag or faster reload.