Adaptive Tactical Shell Carrier, Fits Mossberg 500/590/88, 12 Gauge AT-06000-M Simple and sturdy" the Adaptive Receiver Mounted Shell Carrier for Mossberg keeps six 12 gauge shells at the ready. No need to fumble for shells" just quickly and conveniently reload right from the side of the receiver. Whether for home defense" sport shooting or law enforcement use" the durable shell carrier is up to the task and ready to perform in the harshest of conditions.