An RPG has a small explosion go off in the barrel sending the grenade a short distance before the rocket ignites and carries the grenade the rest of the way to its target. A bowling ball mortar works different. The main charge in the barrel explodes sending the projectile on its way, there is no other propulsion, there is a much greater amount of pressure in that barrel when firing round shot than RPGs. those barrel walls are way too thin, this is a disaster waiting to happen and those look like alot of innocent onlookers! Dear God I hope you know what your doing!
