Ammo Modifications are a special kind of Marine Modification that increase the character's damage potential. They will increase both his weapon's damage, AND the damage of a character's skills. This only applies to abilities actually used by the character, like a Marksman's One Shot One Kill, or a Rifleman's Grenades. It will not effect a skill indirectly used by a character such as an Engineer's Overdrive or Disruptor Towers. An ammo mods base damage, or attack speed bonus will stack, but the bonus effects, such as HE ammos burn, or AP ammos armor debuff will not.