<p>Keep your spare shotgun shells right where you need them with the Monstrum Side Mounted Shell Holder with Picatinny Rail Mount. Built for use with Mossberg 500 and 590 Series shotguns, the shell holder accommodates up to six 12 gauge or seven 20 gauge shotgun shells.</p> <p>Available in two different sizes - one for 12 gauge shotgun shells and one for 20 gauge shotgun shells.</p> <p>The shell holder pairs with a 13 slot Picatinny rail mount that secures to the top of your shotgun. The rail mount is compatible with all Picatinny or Weaver standard scopes, red dots, and optics.</p> <p>The two piece design is built to be mounted together as a single unit. Shell holder or rail mount will not install as stand alone units using the included mounting hardware. Unit installs into the factory mounting holes of Mossberg 500 or 590 Series shotgun models with no additional gunsmithing required. Also compatible with Mossberg Shockwave, 535, 835, and 590a1 models. Please note that pre-1997 Mossberg shotguns were manufactured with a different mounting hole pattern and will require 6x48TPI screws (not included). </p> <p>Rail mount is machined from 6061 grade aluminum. Shell holder is crafted from lightweight polymer. All Monstrum mount and accessory products are backed by a lifetime warranty.</p><p> Compatible with:</p><p> Mossberg 500</p><p> Mossberg 535</p><p> Mossberg 590</p><p> Mossberg 590 Shockwave</p><p> Mossberg 590a1</p><p> Mossberg 835</p><p> Not compatible with:</p><p> Pre-1997 Mossberg shotguns | Requires 6x48TPI screws not included</p><p> Mossbergs without pre-drilled and tapped receivers | Requires drilling and tapping receiver</p><p> Mossberg Maverick 88 | Requires drilling and tapping receiver</p><p> Mossbergs with Crimson Trace LS250 installed | Requires M4-.70 x 12 screws not included</p><p> Mossberg 930 | Requires modifications </p><p> Mossberg 500 Flex | Requires modifications</p>