It's a barrel cover. Bungee cord is replaceable, tho it looks like it might be difficult. Graphics are nice. Doesn't look like it should have trouble fitting over most.
Amazon.com: Exalt Paintball Bayonet Barrel Condom/Cover - LE Thug Life: Sports Durable rubber construction Adjustable, replaceable cord—no plastic.
Exalt Paintball Bayonet Barrel Condom/Cover - Red/Black in Barrels. Durable rubber construction; Adjustable, replaceable cord; Breaks paint that is.