Abstract: Sights for regulating double rifles, and shotguns firing rifled slugs, to converge projectile impacts of the two barrels. Several distinct embodiments activated by inertia or the firearm's mechanism, all providing two adjustable sight leaves, one to be aligned with the impact point of each barrel. In the preferred embodiments the upstanding sight used for aiming a first shot is exchanged at the shot for the second sight by recoil inertia harnessed in one of three ways. One embodiment is reset by cooperation with the firearm but alternated by inertia, while another inertia type is reset manually. A detachable embodiment is provided for shotguns with ventilated ribs, which is both alternated and reset by inertia. A sight activated solely by the firearm's mechanism is also provided.