A grenade is first muzzle loaded into the barrel, the weapon is aimed, then the self-cocking trigger is pulled to fire the weapon. This fires the percussion cap at the base of the grenade which triggers the nitrocellulose propellant inside the body of the grenade. The hot expanding gas from the propellant is forced through vents in the base of the grenade that move the grenade along the barrel, and at the same time force the driving band to engage with the twelve rifling grooves. The rifling imparts stabilizing spin to the projectile.