It works in standard 5.56 AR magazines and with AR-15 bolts. All you need to do to change your 5.56 to an 300 BLK is swap barrels, though most shooters opt for a separate upper receiver.

300 Blackout version below. The Lever Action Supreme packs in patented technology, like a smooth, rotating, multi-lug bolt action, free-floating barrel, and match-grade adjustable trigger.

The MVP Patrol Professional Series from Mossberg is an AR-magazine compatible, bolt-action rifle available in 5.56mm NATO/223 Rem, 300 AAC Blackout ... and threaded barrel with A2-style muzzle ...

300 Blackout, the LASR represents the culmination ... paired with the blued steel free-floated barrel, exceptional accuracy. Out of the box, the Supreme ships with a 10-round Magpul® PMAG ...