Abstract: The present invention discloses a method and system of loading an in-line muzzle-loading firearm. A projectile is rammed into a muzzle end of a barrel of the in-line muzzle-loading firearm such that a bottom portion of the projectile is adjacent or in close proximity with the breech end of a breech plug. A pre-measured powder cartridge is then inserted within a cartridge receiving bore of the breech plug such that a forward end of the pre-measured powder cartridge is adjacent a bottom portion of the projectile and a rim of the cartridge engages a first annular lip of the breech plug. The cartridge may then be secured within the breech plug by action of a bolt mechanism or a break open receiver mechanism.