The refill cartridges make it easy to reload your Mace Brand Pepper Gun. Simply follow these three quick steps: 1. Push the barrel release on the side of the gun forward and open the barrel. 2. Grasp the exposed portion of the old cartridge and gently pull outward to remove it from the barrel. 3. Insert the new cartridge into the barrel, being careful not to press onto the cartridge, then close and lock the barrel.