An ammunition system for a firearm includes a cartridge for a firearm, a muzzle-loaded cartridge attachment, a magnet, and a magnetic material. The muzzle-loaded cartridge attachment is loaded into the barrel after the cartridge is loaded in the usual manner. The two are adhered together by magnetic attraction. The cartridge has the magnet, the muzzle-loaded cartridge attachment has the magnet, or both have magnets aligned to draw the two together. When one magnet is present between the two, then the other must have a magnetic material to be drawn to the magnet. To enable more than one muzzle-loaded cartridge attachment to be added, a third magnet may be used within the muzzle-loaded cartridge attachment at the end opposite the cartridge to exert a magnetic field extending toward the muzzle, which will hold the next muzzle-loaded cartridge attachment added to the barrel.