Mesa Tactical SureShell Carrier, 6-Shell Side Saddle, Fits Mossberg 500, 12 Gauge, On-gun shotshell carriers, Black Finish 94750 This SureShell Polymer Carrier system features shell holders injection molded from glass filled polymer and secured to the receiver by a lightweight aluminum back plate with brass threaded inserts. The new SureShell Polymer Carrier also includes an innovative dual rubber friction system that reliably holds shotshells in place.