Tiger Rock AR-15 Barrett Style Muzzle Brake with Jam Nut Long. The Tiger Rock AR-15 Barrett Style Muzzle Brake w/ Jam Nut includes a jam nut which is a must-have with any shooting system setup as the jam nut not only keeps the device from spinning but it holds the o-ring in place as well. So if you are looking for a great way to make sure you are shooting with the best look no further than the Tiger Rock AR-15 Barrett Style Muzzle Brake w/ Jam Nut. Package Contents: Tiger Rock AR-15 Barrett Style Muzzle Brake with Jam Nut Tiger Rock MBR62LONG: AR-15 Barrett Style Muzzle Brake with Jam Nut (NEW) Long