M27 IAR U.S Marines with their new H&K M27 IAR (Infantry Automatic Rifle). Marine Corps regulation states that only standard issue U.S.G.I 30 round magazines will be used in the IAR. As for the M249 being unreliable; that is true to some extent. A majority of the M249’s in service are aging and well-worn, if not completely worn out. Replacing parts and upgrades have been slow, considering the M249 has been in service for over 25+ years.