In the year 2000 Beretta introduced the 12-gauge Optima Bore barrel design into some of our competition shotguns. This new barrel utilized a larger internal bore dimension known to some as “back-boring” and required a new choke tube design to give the proper constrictions. The Optima barrels can be identified by locating the letters “OB” stamped next to the barrel gauge stamp. Barrels marked with the “OB” stamp will use the Optima-Choke system. This design features a longer internal transition taper into the choke constriction, making the overall length of this tube longer than the original Mobilchoke tube.