Carlsons Winchester 20ga Flush Replacement Full 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, copper-plated, nickel, hevi-shot, or bismuth may be used in these choke tubes. Fits 20ga Winchester/Browning Invector/Mossberg 500 choke systems Manufactured from 17-4 Heat Treated Stainless Steel Can be used with Steel, Lead, Hevi-Shot, or Bismuth ammo Lifetime Warranty