This unique product seals the chamber and bore to prevent solvents and oils from running back into the action when the rifle is left in an upright position. For heavily fouled barrels, we use these plugs to seal the chamber and then fill the barrel with our favorite solvent. Then we let the barrel sit for a while. If left overnight, you should seal the muzzle end with tape to prevent evaporation. Make sure you fill the barrel all the way to the muzzle end. If storing guns for a long time, these plugs can keep rust preventative agents and oils from seeping down into the action and trigger group area. Oil and debris washed in with excess solvent harms more triggers than just about anything. Replacement O -rings come in packs of 5.