Mesa Tactical SureShell, 4-Shell Side Saddle, Fits Moss 500/590A1/Mav88, 12 Gauge, Left Side, Matte Finish, Black 91240 SureShell shotshell carriers are available in three configurations: four-shell" six-shell and eight-shell configurations that can be installed on the left side of the receiver. Carriers can also be installed pointed back toward the stock. The principle difference between one model of SureShell and another" aside from capacity" is the backing plate" which is designed to mount the carrier assembly on a particular model of shotgun. Side-mount SureShell shotshell carriers for Mossberg " Remington and Benelli M1 shotguns use the trigger group pin holes to secure the assemblies to the weapon; the Benelli M2 Tactical" Benelli M4/M1014" Benelli SuperNova Tactical and some Mossberg 500/590 versions take advantage of the factory-tapped rail mounting holes in the tops of these shotguns and include integrated Picatinny optics mounting rails; another version with an integrated rail is the saddle-mount design for Remington; SureShell Carriers for M4 SOPMOD stocks feature special hardware for attachment to these buttstocks; Adapter Mount SureShell shotshell carriers are designed to be attached to Mesa Tactical Telescoping Stock Adapter accessory mount points.