Carlson's Beretta/Benelli Mobil 20ga Flush Improved Cylinder Choke Tubes are made of 17-4 heat treated stainless steel. Steel or lead shot may be used in these choke tubes. Steel shot larger than bb should not be used in any choke tighter than full. lead, copperplated, nickel, hevi-shot, or bismuth may be used in these choke tubes.