8th Commandment of Firearm Safety
Be sure the barrel is clear of obstructions before shooting.
Before loading your gun, open the action and make sure there's no ammunition in the chamber or magazine. Check the barrel for any obstructions or debris. Even a small amount of snow, mud, excess lubricant or grease in the bore can dangerously increase pressure and cause the barrel to bulge or burst when firing. Use a cleaning rod and patch to wipe away anti-rust compounds or any other residues or obstructions in the barrel. Never try to shoot out an obstruction by loading another shell and firing!
When firing, rely on your instincts. If the noise or recoil from your firearm seems off or weak, stop everything, unload your firearm and be sure nothing is lodged in the barrel. Remember the 12/20 burst? That's what can happen when the barrel is obstructed. So always be sure you're using the correct ammunition in your firearm and that it's free of obstructions.