The MB47 is patterned after the original milled Bulgarian receivers but with the added feature of an integrated AR buffer extension. Each 2 pound receiver is machined from a solid 15 pound block of US sourced 4140 steel, then heat treated to an RC41 hardness. Barrel journal is reamed to .9065 post heat treat for absolute perfection. The receiver is compatible with any milled AKM parts kit or any standard, stamped AKM parts kit. Target interference between barrel and barrel journal is .001" Absolute max would be .0015".