TacFire RK300LPK: TacFire\'s AR-300 Blackout Unassembled rifle build kit includes a black nitride barrel with a 1/2\"-28 A2 flash hider; a Slim M-Lok free-float handguard; upper receiver; 300blk/5.56 bolt carrier group; charging handle, dust cover, forward assist, pistol length gas tube, .750\" gas block; lower parts kit with trigger and hammer; 3oz buffer; buffer spring; castle nut; end plate; six-position stock; A2 pistol grip all made in the USA. This model has a 7.5\" barrel.