This unique product seals the chamber and bore toprevent solvents and oils from running back into theaction when the rifle is left in an upright position.For heavily fouled barrels, we use these plugs to sealthe chamber and then fill the barrel with our favoritesolvent. Then we let the barrel sit for a while. If leftovernight, you should seal the muzzle end with tapeto prevent evaporation. Make sure you fill the barrelall the way to the muzzle end. If storing guns for along time, these plugs can keep rust preventativeagents and oils from seeping down into the actionand trigger group area. Oil and debris washed inwith excess solvent harms more triggers than justabout anything. Replacement O -rings come in packsof 5.