ammunition for the 90 mm rifle was issued in complete fixed cartridges. the term "fixed" means that the projectile and the cartridge case are crimped together. this ensures correct alignment of the projectile and the cartridge case. it also permits faster loading because the projectile and the cartridge case are loaded as one unit. the rear end of the cartridge case is made of frangible material that is completely destroyed when fired. the projectiles used are pre-engraved with a rifling band, that is, the rotating bands are cut to engage the rifled bore both to trap gases and to spin-stabilize the projectile.