Carlson's Sporting Clays Choke Tubes are made from 17-4 stainless and precision machined to produce a choke tube that patterns better than standard choke tubes. These choke tubes feature a 25% larger parallel section in the choke, thus throwing more consistent patterns than conventional choke tubes. Lead, Copperplated, Nickel Hevi-Shot(TM), Bismuth, Tungsten or Steel Shot may be used in these choke tubes. For best results, pattern your choke tube with the specific shotshell load you will be using in the field. Different ammunition patterns differently from the same choke tube. Mfg: Carlsons