Aridus Industries CROM Optic Mount (Mossberg 500/590/930)

The Aridus Industries CROM (Co-witness Ready Optic Mount) is the lowest and most rigid way to mount a red dot on a Mossberg 500, 590, 590A1, or 930. Instead of a Picatinny rail mount that perches the optic well above the bore, the CROM bolts directly to the factory drilled and tapped holes on the top of the Mossberg receiver. This drops the optic height by roughly 0.4 inches versus a typical Picatinny mount, putting the dot in line with the natural cheek weld instead of forcing the shooter to lift their face off the stock.

The CROM accepts any Trijicon RMR footprint optic, which includes the Holosun 507C, 407C, and 508T as direct-fit alternatives. The mount has an integrated XS rear ghost ring sight that gives an emergency backup sighting system: pair the CROM with an XS Big Dot tritium front sight (~$88), and the shooter has both an electronic dot and an iron co-witness on a single unit. If the optic battery dies or the dot fails, the ghost ring is immediately available without removing the optic.

Installation requires the factory drilled and tapped holes on the receiver, which is standard on the 500, 590, 590A1, 590S, and 930. Any Mossberg shotgun manufactured in the last 20+ years has these holes; older guns or some 500 budget variants may not, so verify before ordering. Installation uses the supplied screws and Loctite (do NOT skip the Loctite, the receiver is heat-treated steel and threads strip slowly under recoil if the screws back out).

The trade-off vs a Picatinny rail mount is versatility: the CROM is RMR-footprint only, so swapping to a different optic family (Aimpoint Micro, Acro) means buying a different mount. For shooters committed to the RMR footprint (which is the dominant pistol/shotgun red dot footprint), that is a non-issue. For builders who want to run an Aimpoint Micro and sometimes a magnifier or Picatinny accessory, the Scalarworks SYNC mount on the factory rail is the better answer.