Caliber: 5.56 NATO. Capacity: (1) 20-round metal. Barrel: 15.5 in.; 1:12 RH twist. A1-profile, standard 3-prong "duckbill" flash hider. Upper/Lower Receivers: Machined 7075 T6 aluminum receivers. XBRN16E1 lower has partial "fence" around the magazine release. Upper has forward assist, but no shell deflector. Stock: Fixed “Type D” buttstock. Sights: Windage-adjustable A1-type rear sight drum. Weight: 7.5 lbs. Overall Length: 34 in. Features: Colt's first carbine variant of the M16 rifle. Black furniture of reinforced polymer, triangular cross-section handguard. As of 2022, only available as a build kit, not as a complete rifle.