 In the original Metal Storm patents, the propellant immediately behind the projectile closest to the muzzle of the gun barrel was ignited by an electronically fired primer, the projectile was set in motion, and at the same time a reactive force acted on the remaining stacked projectiles in the barrel, pushing them backwards.By design, the remaining projectiles would distort under this load, expanding radially against the gun barrel wall.This created a seal ("obturation"), which prevented the hot propellant gases (expanding behind the lead projectile) from leaking past them and prematurely igniting the remaining propellant charges in the barrel.