Continuing with my Heaven in Camo weekend, this morning I got to fire a half dozen rounds from an M203 Grenade Launcher--the standard grenade launcher for all army units. M203 is the designation for the entire weapon. The grenade launcher itself is the 12-inch tube underneath the barrel of the rifle or carbine it is attached to.
The weapon fires 40mm grenades and loads like a shotgun. We fired dummy rounds. The live rounds are high explosive and have a kill radius of 5 meters so you don't have to make a direct hit to be effective.