The Brownells BRN-4 5.56mm complete upper receiver with 14.5" medium barrel and 13.5" handguard is a purpose-built AR platform upper that arrives ready to bolt onto your lower—no gunsmithing required. Built from the ground up with new-manufacture components, this is a plug-and-play upper for shooters who want quality construction without the assembly hassle. Whether you're building a duty rifle, a precision trainer, or a dependable range gun, the BRN-4 gives you a solid foundation with proven ergonomics and balanced performance.
The heart of the system is a custom bolt carrier group machined from forged 8620 steel with a 9310 tool steel bolt—both components are headspaced before and after barrel installation to ensure reliability. The Faxon-made barrel features a 1-7 twist rate optimized for the full spectrum of 5.56x45mm NATO ammunition, and the medium profile strikes a practical balance: enough steel to handle repeated firing strings without grouping degradation, yet light enough to keep the overall package manageable. The gas block is vented forward to minimize rearward gas signature, and it's matched specifically to the 14.5" barrel length for predictable operation.
The upper receiver itself is machined from billet aluminum, then hard-coat anodized in matte black. Extended barrel nut threads engage the barrel extension over a larger surface area than standard AR uppers, creating a rigid interface that Brownells torques and verifies three times during final assembly. The 13.5" Midwest Industries handguard offers abundant M-LOK slots and a full-length Picatinny rail, so you can mount lights, lasers, or grips exactly where you need them. The charging handle is mil-spec, and a Magpul ejection port cover is included. All uppers ship test-fired, so you may see brass marks or light fouling—a mark of quality control, not a defect.
For optimal function, Brownells recommends pairing this upper with an H1 or H2 recoil buffer and carbine recoil spring on a compatible lower receiver. Use quality 5.56x45mm NATO ammunition for the most reliable results.
| Caliber | 5.56x45mm NATO |
| Barrel Length | 14.5" |
| Barrel Profile | Medium |
| Barrel Twist | 1-7 |
| Muzzle Threading | 1/2-28 |
| Handguard Length | 13.5" |
| Handguard Brand | Midwest Industries |
| Upper Receiver Material | Billet aluminum, hard-coat anodized |
| Carrier Group | Forged 8620 steel carrier, 9310 tool steel bolt, nitride finish |
| Charging Handle | Mil-spec |
| Accessories Included | Magpul ejection port cover |
This complete upper is designed to attach to a standard AR-15 lower receiver. Ensure your lower is properly assembled and functional before mating it to this upper.
Yes. The upper includes a complete custom bolt carrier group with forged 8620 steel carrier and 9310 tool steel bolt, both headspaced and ready to fire.
Brownells recommends an H1 or H2 recoil buffer paired with a carbine recoil spring for optimal operation on a compatible lower.
Yes. All BRN-4 upper assemblies are test-fired before final packaging. You may notice brass marks on the shell deflector or light fouling inside, which is normal and indicates the upper has been quality-checked.
Brownells
Brownells
