 The rearward seal to the skirt is provided by the nose of the following projectile in the barrel.As in the previous design, the firing of a projectile results in a rearward impulse on the remaining projectiles stacked in the barrel.This results in the skirts of the remaining shells in the barrel being compressed against the following shell heads, effectively creating a seal that prevents hot gases in the barrel triggering unintended propellant ignition ("blow-by") along the length of the barrel.