Keep your spare shotgun shells right where you need them with the Patent Pending Monstrum Side Mounted Shell Holder with Picatinny Rail Mount. Built for use with Mossberg 500 and 590 Series shotguns, the shell holder acco...

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Keep your spare shotgun shells right where you need them with the Patent Pending 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 shotgun shells. The ambidextrous design allows for installation on either side of the stock for shooters of all orientations.

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.

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).

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.



  • Built for use with Mossberg 500, 590, and Shockwave Series shotgun models
  • Not compatible with Mossberg 500 Bantam, Mossberg 500 Combo, Mossberg 500 Flex Models or models where the pump action extends past the receiver when pumped. See attached infographic before purchasing. Pre-1997 Mossberg shotguns were manufactured with a different mounting hole pattern and will require 6x48TPI screws (not included).
  • Shell holder available in two sizes - 12 gauge saddle accomodating up to six 12 gauge shells and 20 gauge saddle accomodating up to seven 20 gauge shells
  • Rail mount allows for the mounting of Picatinny or Weaver standard scopes, red dots, or other optics
  • Installs via included set screws into the Mossberg factory mounting holes with no additional gunsmithing required
  • Built for use with Mossberg 500, 590, and Shockwave Series shotgun models
  • Not compatible with Mossberg 500 Bantam, Mossberg 500 Combo, Mossberg 500 Flex Models or models where the pump action extends past the receiver when pumped. See attached infographic before purchasing. Pre-1997 Mossberg shotguns were manufactured with a different mounting hole pattern and will require 6x48TPI screws (not included).
  • Shell holder available in two sizes - 12 gauge saddle accomodating up to six 12 gauge shells and 20 gauge saddle accomodating up to seven 20 gauge shells
  • Rail mount allows for the mounting of Picatinny or Weaver standard scopes, red dots, or other optics
  • Installs via included set screws into the Mossberg factory mounting holes with no additional gunsmithing required

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