The Colt M4 Upper Receiver is a factory-produced 5.56 NATO upper assembly designed for AR-15 platform lowers.
- Caliber: 5.56 NATO / .223 Remington
- Type: Complete upper assembly
- Compatible Lower: Mil-spec AR-15
- Barrel Length: 16 inches
- Material: 7075-T6 aluminum receiver
- Finish: Black anodized
- Includes: Barrel, front sight, handguards, charging handle, bolt carrier group
- Installation: Drops onto mil-spec lower, requires takedown pin alignment










