Deep Impact

The Deep Impact perk allows you to shoot through higher density materials such as brick, metal sheeting, concrete blocks (not solid concrete walls), all with reduced damage. It also causes more damage when shooting through lighter materials like wooden fences and drywall. However, it does not inflict more damage to an exposed enemy than it normally would.

Deep impact will give you a slight increase in damage when firing through walls without the stopping power perk. However there remain some materials that just can never be shot through, so don't get the idea that Deep Impact allows you to shoot through everything.

Additional Multiplayer Tactics
Deep Impact is a favorite among snipers and light machine gunners. It can also be very effective with players who can expertly read the minimap and know common hide spots. It can be used to take players behind cover at long ranges or clear a room/hallway without ever entering it. Learning how the players use cover and keeping an eye on the map can provide an easy target. When fighting from a window it is smarter to move to the back wall or leave the room completely. Remember that crosshairs will provide a hit indication so if a player is stuck behind an object it may be better to get up and make a break for it.