TacFire Unassembled Rifle Build Kit AR-15 5.56x45mm NATO 16in Barrel 15in Handguard 1-8 Twist 1/2x28 A2 Birdcage Black RK556LPK. With a 1:8 twist rate your new firearm will stabilize everything from 55-grain range ammo to 69 plus grain match...