Advanced Technology International Halo Side Saddle gives Mossbergs (500-590) a modular nine-piece side saddle for holding extra shells and mounting optics. It easily mounts to the shotgun with pre-existing top mounting holes. Any 500 or 590 without pre-existing top mounting holes will require gunsmith services. The military Type III anodized 6061 T6 aluminum constructed Halo mount uses existing screw holes in the top of the receiver. Its sleek skeletonized side saddle design weighs only 5.5 oz. There are three mounting locations on the ejection port side, six on the non-ejection port side, and a mounting location for a 6-inch top rail. This gives a shooter the ability to firmly secure nine shells in any configuration and mount optics or other accessories on top of the weapon system. Halo is manufactured in the USA and has a limited lifetime warranty.