Described herein are examples of drop-in full automatic trigger groups. A drop-in full automatic trigger group may be configured for installation within a lower receiver of a firearm. The trigger group may a housing defined by a first trigger pin hole, a first hammer pin hole, and a first sear pin hole; a second trigger pin hole substantially collinear with the first trigger pin hole, a second hammer pin hole substantially collinear with the first hammer pin hole, and a second sear pin hole substantially collinear with the first sear pin hole. The trigger group may include a trigger mechanism disposed at least partially within the housing. The trigger group may include a hammer mechanism disposed at least partially within the housing. The trigger group may include a sear mechanism disposed at least partially within the housing.