A combustion powered, pneumatic augmented gun system is disclosed. The combustion powered, pneumatic augmented gun system may include a gun barrel, a combustion chamber, an augmentation air plenum in fluid communication with the combustion chamber, a trigger valve assembly, a fuel supply tank connected to the combustion chamber disposed to provide a combustible fuel to the combustion chamber, and an air compressor connected to the augmentation air plenum disposed to provide compressed air into the augmentation air plenum. When a projectile is to be fired, fuel is combusted in the combustion chamber providing a flow of gases into the gun barrel. Compressed air from the augmentation air plenum is released to augment the acceleration of the projectile in the gun barrel when pressure in the combustion chamber drops.