Heavy machine gun (Tome of tech supplement)
From D&D Wiki
This heavy machine gun uses 7.62.54mm ammunition in 250-round belts. Although a single person can fire a heavy machine gun, it typically has a two-person crew: the gunner, and a loader who assists with feeding the ammunition belt into the weapon. As a full-round action, the loader can use a special aid another action to grant the gunner a +2 bonus on his next attack roll. Because of its size and heavy weight, this gun is often either mounted on a wheeled chassis with a gun shield for trench defensive use, or on the back of a horse-drawn wagon. Assuming a user can even lift the weapon, firing a heavy machine gun machine gun that is not mounted imparts a –4 penalty on attack rolls and the recoil knocks the wielder prone. The machine gun is automatic-fire only. The armored shield provides cover when firing the weapon from the prone position.