This paper model is a M79 Grenade Launcher, a single-shot, shoulder-fired, break-action grenade launcher that fires a 40x46mm grenade, which uses what the US Army calls the High-Low Propulsion System to keep recoil forces low, and first appeared during the Vietnam War, the papercraft is created by ruthus18.
Because of its distinctive report, it has earned the nicknames of "Thumper", "Thump-Gun", "Bloop Tube", and "Blooper" among American soldiers; Australian units referred to it as the "Wombat Gun". The M79 can fire a wide variety of 40 mm rounds, including explosive, anti-personnel, smoke, buckshot, flechette, and illumination. While largely replaced by the M203, the M79 has remained in service in many units worldwide in niche roles. For further information of the M79 please click here.