Abstract: A cylindrical alongated extender element (20,60,72,80) of various incremental lengths has a bore (22) and a first end portion formed with a sleeve portion (24) and threaded portion (26) adapted to be received in the choke receiving seat (14) formed in the bore of a shotgun barrel. A sight (46) is mounted on a rib (40, 68, 76) which is coextensive in length with the extender elements to provide an improved sight picture. The extender elements are adapted for use with a single barrel gun or a double barrel over-and-under and side-by-side arrangements. With the over-and-under arrangement a rib assembly having a single tubular portion mounting the rib is mounted on an adaptor seat of one of the extender elements and with the side-by-side arrangement a rib assembly has first and second tubular portions mounting the rib and received on adaptor seats of two extender elements. The extender elements can optionally, in turn, be provided with choke receiving seats.