The MVP uses AR-15 magazines. Says so in the manufacturer's literature. As a result, the largest capacity magazine you will be able to use will either be the 10 round LAR-15 mag, or the 5 round. 50 Beowulf that apparently will accept anywhere from 14-18 rounds, depending on who you talk to. Any unpinned standard 10 (other than the RRA LAR-15), 20 or 30+ round AR mag is considered a prohibited device and if caught with one will result in some pretty serious charges and legal consequences. It doesn't matter if you're using it in a bolt action rifle instead of an AR. As the law is written right now, if the MVP will accept the. 50 Beowulf or the LAR, you're golden.