Bismuth is a popular material used in shot shells throughout the industry.This shot performs best when paired with the rraptor biz choke.This choke is a strong addition to the rraptor series.These choke tubes are built from years of product development and innovations using the highest advanced technology available.They are made out of 17-4 ph u.S.Stainless steel.*over-shotguns can have a rraptor choke in only one barrel.The design of the choke does not allow for placement in both barrels*Gauge: 12 GaugeMaterial: 17-4 PH Stainless Steel