These choke tubes are designed and manufactured for top quality performance while shooting Hevi-Shot loads (bismuth and tungsten matrix.) This product has been field tested for optimum diameter producing super full choke patterns. (Puts 90% of the shot, in a 30" circle at 40 yards.) The Undertaker H.S. is manufactured in 41L42 chrome-moly, aircraft quality alloy and heat treated to handle those tough new loads. It has a blued finish and is double knurled for easy hand installation. Available for the Benelli M2 20-gauge shotgun & for both high density shot and lead and copper plated shot, and ported and unported. Featuring a blued finish, 3" long tube, these chokes have a knurled end for hand installation.