Brownells Brn-4/M27 5.56X45 16.5'' Medium Chrome Lined Barrel Phosphate

The Brownells BRN-4/M27 5.56x45 barrel is a 16.5-inch performance upgrade purpose-built for the BRN-4 platform and compatible HK-pattern receivers. Manufactured by Faxon, this chrome-lined, manganese phosphate-finished barrel delivers the M27-inspired configuration shooters have been asking for, combining a robust 1-7 twist bore with a forward-mounted bayonet lug for tactical or historical accuracy builds. Whether you're upgrading an existing upper or building from scratch, this barrel brings genuine military-heritage features to a modern platform.

Built from 4150 chrome moly steel with a precision-buttoned bore, the barrel chamber is chrome-lined for durability and corrosion resistance—a practical choice for shooters who run hard-use ammunition or train in demanding conditions. The ½-28 threaded muzzle accepts standard A2 flash hiders or any common AR15-pattern muzzle device, giving you flexibility in your setup. The M4 feed ramps accommodate a full range of .223 and 5.56 ammunition, so you're not locked into one type of round.

The forward bayonet lug is a distinctive feature: it installs the same way as the gas block, with a simple coil pin driven from the side, creating an extremely robust mount. This design makes the bayonet attachment one of the most solid options available. Keep in mind you'll need a BRN-4 16-inch gas block to run this barrel properly, and the lug installs after the gas block is mounted.

Compatible with Brownells BRN-4 upper receiver groups, as well as HK, 416, MR556, and MR223 platforms, this barrel opens up options if you're working across multiple rifle platforms or planning a modular build.

Key Features

• M27-inspired configuration with forward-mounted bayonet lug
• Chrome-lined 5.56x45 NATO chamber for corrosion resistance and longevity
• Precision 1-7 twist buttoned bore for accuracy and reliability across ammunition types
• 4150 chrome moly steel construction with manganese phosphate finish
• M4 feed ramps for broad ammunition compatibility
• ½-28 threaded muzzle for standard A2 or aftermarket devices
• Bayonet lug installs simply with coil pin—robust and field-proven design
• Compatible with BRN-4, HK, 416, MR556, and MR223 platforms

Specifications

Frequently Asked Questions

Is this barrel compatible with my HK 416 or MR556?

Yes. While designed for the Brownells BRN-4 platform, this barrel is also compatible with HK, 416, MR556, and MR223 receivers, making it a versatile choice if you're building across multiple platforms.

What gas block do I need for this barrel?

You'll need a Brownells BRN-4 16-inch gas block. The bayonet lug installs after the gas block using the same coil-pin method, so proper gas block fitment is essential.

Can I use the standard A2 flash hider from an M27?

Yes. The barrel features ½-28 threads, which accept the standard A2 flash hider found on the M27, as well as any common AR15-pattern muzzle device.

What ammunition will cycle reliably through this barrel?

The M4 feed ramps and chrome-lined chamber are designed to work with a wide range of .223 and 5.56 NATO ammunition, giving you flexibility in what you run.