Magblock for the LaRue Tactical 20 round AR-10 Magazines. Made of heat and impact resistant fiber reinforced polymer. Won't deform even in the most hostile environments. This is the same as the M14 Limiter. Will be a tight fit in the base. Thanks to EBR Works for this compatibility update. Check them out at for compliance work:  http://www.ebrwebstore.com/middleman-ffl-services