Magnum Ammunition (MGNM AM), commonly abrreviated to Magnum Ammo, is a specialization in Battlefield: Bad Company 2's multiplayer, unlocked at Rank 15, Staff Sergeant III. It increases all firearm damage by 25%.
The Magnum Ammo specialization is coupled to the player, not the weapon. If a Magnum Ammo user were to acquire a new weapon on the field, this specialization would still be in effect. Likewise, if a player were to scavenge a weapon belonging to a Magnum Ammo user, they would not gain its effects.
Magnum Ammunition is canceled out by Ceramic Body Armor, because Ceramic Body Armor gives a health increase while Magnum Ammunition gives a damage increase.
Magnum Ammunition is useful on many weapons as it allows the player to kill a target with fewer shots, hence faster and more efficiently. It is popular among shotgun users (especially pump-action shotguns) as it increases the damage of the pellets, allowing the player to kill the target with fewer pellets and at slightly farther ranges. Magnum ammo can be useful for Recons who use bolt-action rifles or players that use shotguns with 12 Gauge Slugs to ensure one-hit kills against players using Ceramic Body Armor, or up to 20.4m (where without Magnum Ammo, they would do 80 damage) or 26m for the M95 against players without it. Beyond those ranges, only a headshot can ensure one shot kills, hence making Magnum Ammo relatively useless for long range sniping, although in Hardcore mode Magnum Ammo ensures a bolt-action rifle or pump-action shotgun with slugs user a one-hit-kill at all ranges, regardless of shot placement.
Contrary to common belief, Magnum Ammunition does not affect bullet drop, nor does it create vapor trails. It also increases the damage of the Flamethrower, despite the Flamethrower not being a projectile weapon.