Luth-AR 18 in Mark 12 kit minus Lower Receiver w/fixed stock Black Rifle RKM12-18-1M. 56mm Overall Length: 28 in Barrel Length: 18 in Barrel Profile: Heavy Barrel Twist Rate: 1-9 Threads per Inch: 1/2x28 Handguard Type: Free-Float Muzzle Device: A2...