This kit essentially provides a conversion to 590S functionality, but in a more robust design. It contains our patent-pending Universal Cartridge Adapter and low-drag no-snag Magazine Follower which allows smooth cycling of 1-3/4" Minishells up to 3" Magnum cartridges in the same magazine. The adapter is constructed from vulcanized thermoplastic rubber, and the follower is machined from solid 6061-T6 billet aluminum. This kit is compatible with any Mossberg 12-Gauge pump-action firearm with a 3" Chamber and machined grooves in the receiver. Please refer to the picture below or the installation video below to confirm your firearm's compatibility.