Instructions
Equip a shotgun by pressing "X" on the PS3 controller after killing an enemy who has a shotgun. A shotgun is a close-range weapon. You can only carry two weapons at a time, so it's wise to carry a mid- to long-range weapon as your secondary, like an AK-47 or a Dragon Sniper.
Pull out the shotgun using the "D-Pad" on the PS3 control when in tight corridors. Use the targeting reticle to aim at the enemy's chest.
When enemies are only a few feet away from you, fire the shotgun from the hip by pressing "R1" on the PS3 controller.
Resist firing the shotgun until the enemy is as close as possible for a guaranteed one-shot kill.
Switch to your mid- to long-range weapon when back in an open area; if an enemy gets too close, quickly switch back to the shotgun to kill with one powerful blast.