TacFire SS-RK556-LPK 556 RFL BUILD KIT SSRK556LPK. 56 Nato M4 contour barrel/nitride; birdcage flash hider w/crush washer; 15" MLOK free float handguard; AR15 5.56/.223/.300AAC stripped billet upper receiver w/M4 feed ramps/.556 Mil-Spec charging...