 In addition to the pioneering Nitro Express cartridge, Rigby was also noted for the unique vertical-bolt or rising-bite action, used only on its best-grade double rifles and shotguns.Based on the Rigby-Bissell Patent of 1879, this is a complex and massively strong locking system with a post that rises vertically out of the break-off into a U-shaped loop extending rearward from the top rib of the barrels, as a third fastener.Between 1879 and 1933, Rigby built approximately one thousand rising-bite guns and rifles in many different bores.