Carlson's Browning Invector Plus 12ga Sporting Clay Modified Choke Tubes are made from 17-4 heat-treated stainless steel and are precision machined to produce a choke tube that patterns better than standard choke tubes. These choke tubes feature a 25 percent longer parallel section in the choke thus throwing more consistent patterns than conventional choke tubes. Extended choke tubes protect the end of your barrels and have knurling on the end to allow for quick and easy removal. Each choke tube has the constriction laser marked on the end for easy reference. lead, copper-plated, nickel, hevi-shot, bismuth, tungsten or steel shot may be used in these choke tubes.