These are the JW Muzzle brakes. These were designed and built for John Wayne Walding to put on his world class bolt rifles. These are builders brakes and "WILL NEED TO BE DRILLED" to the proper size for the particular caliber you are using. They can be tapered or turned down to match the barrel diameter. These have been compared to brakes that cost twice as much and picked as the higher quality. Made of 303 Stainless Steel.