loose barrel key

To tighten a loose barrel key, remove the barrel and peen or bend the underlug to tighten up the slot. Support the barrel on a bench and use a small hammer to tap the top of the underlug. If the key no longer fits after doing this, use a needle file to open up the slot, specifically opening up the side of the slot nearest the barrel. This effectively moves the slot closer to the barrel and tightens the key's fit. Alternatively, a modified underlug with a slot closer to the barrel centerline is available can be installed.