Investor Plus choke tubes come standard in all Browning back-bored barrels. Investor Plus and back-boring work together as a team. The longer choke taper inside an Investor Plus choke tube - combined with back-boring - produces patterns with uniform densities. Investor Plus tubes are for Browning's back-bored 12 and 20 gauge shotguns only, and are not intended for standard bored barrels.