RIFLE: BUSHMASTER FIREARMS MODEL CARBON-15, SERIAL NUMBER CBC050777, BLACK (MATTE), CASE NOT INCLUDED, SEMI - AUTOMATIC, 5.56 NATO, 17 Notes: The Bushmaster Carbon 15 is a lightweight, AR-15-pattern semi-automatic firearm originally developed by Professional Ordnance and later produced by Bushmaster. Its defining feature is its carbon-fiber-composite upper and lower receivers, which were designed to reduce weight compared with conventional aluminum AR-style receivers. Carbon 15 variants were offered in several configurations, with many rifle models chambered for .223 Remington/5.56x45mm NATO. Manufacturer: Bushmaster Firearms; the Carbon 15 design originated with Professional Ordnance. Type: Semi-automatic rifle/carbine family, with some pistol variants. Common caliber: .223 Remington / 5.56x45mm NATO. Operating system: Gas-operated, magazine-fed design on the .223/5.56 models. Receiver material: Carbon-fiber composite, a major distinguishing characteristic of the Carbon 15. Typical rifle barrel: Several models used a 16-inch barrel; specifications vary by exact model. Magazine compatibility: Many 5.56 Carbon 15 rifles accept AR-15/STANAG-pattern magazines, with capacities depending on the magazine and configuration. Weight: Certain R21/R97 variants were notably lightweight, with some listed around 3.9-4.3 lb. Sights/optics: Depending on the model, configurations included Picatinny-style optics rails, adjustable rear sights, and front sights.