The Airsoft Station barrel cover is the last barrel cover you will ever need to buy. It is made to be extremely durable and the opening is wide enough to fit over any barrel or barrel extension. The bungee cord is super thick to make it extra tough. The purpose of a barrel blocker for airsoft is to prevent unintended shots from firing from the gun. Even if the magazine is removed from an airsoft gun there is almost always a BB left in the barrel that can be fired. The blocker goes over the end of the barrel/muzzle and captures any accidental shots. The end of the bag is nylon-reinforced to minimize any chance of BB penetration. A barrel blocker is a mandatory piece of safety equipment at most airsoft fields and is highly recommended to be used with every airsoft gun that you own in conjunction with other safety precautions!