Green Mountain 5.56 AR-15 Barrel 20" M16 A1 Phosphate - GM-M15
$194.95
Only 2 left in stock
Upgrade your AR-15 build with the Green Mountain 5.56 AR-15 Barrel 20″ M16 A1 Phosphate, a precision-engineered component designed for shooters who demand accuracy, durability, and authentic M16-style performance. Crafted to exacting standards, this barrel delivers reliable function in both recreational and tactical applications while supporting modern 5.56 NATO ammunition.
Key Features and Benefits
- Chrome-lined bore and chamber with phosphate exterior finish – Provides exceptional corrosion resistance and extended service life, reducing maintenance needs and ensuring consistent performance in varied conditions.
- Government / SOCOM profile with rifle-length gas system – Offers a balanced weight distribution for improved handling and reduced recoil, ideal for precision shooting or duty use.
- 1:7 twist rate – Optimized for stabilizing a wide range of bullet weights, including heavier projectiles, enhancing accuracy across different loads.
- 0.625″ gas block journal and 1/2×28 muzzle threads – Ensures compatibility with standard low-profile gas blocks and a variety of muzzle devices for custom configurations.
- M16-style extension and 20-inch length – Delivers classic ergonomics and velocity for effective terminal performance at longer ranges.
Technical Specifications
- Platform: AR-15
- Caliber: 5.56 NATO
- Barrel Length: 20 inches
- Twist Rate: 1:7
- Gas System: Rifle length
- Gas Block Journal: 0.625 inches
- Muzzle Thread: 1/2×28
- Finish: Phosphate with chrome-lined bore and chamber
- Barrel Profile: Government / SOCOM
- Weight: 35.4 ounces
Why Choose This Product
This barrel addresses common pain points for AR-15 builders, such as inconsistent accuracy with varying ammunition and premature wear in harsh environments. The robust construction from premium materials ensures tight tolerances for reliable feeding, extraction, and grouping. Whether restoring a classic M16A1 replica or building a modern tactical rifle, it provides the foundation for dependable operation without compromising on quality or compatibility.
Invest in a barrel that combines proven design with contemporary performance enhancements for years of trusted service.
| Weight | 35.4 oz |
|---|---|
| Dimensions | 20 in |
| Finish | Phosphate + Chrome Lined |
| Barrel Profile | Government / SOCOM |
| Cartridge Compatibility | 5.56 NATO |
| Gas Block Journal | 0.625 |
| Barrel Length | 20 |
| Gas System Length | Rifle |
| Platform | AR-15 |
| Twist Rate | 1:7 |
| Muzzle Thread Pattern | 1/2×28 |
| MPN | GM-M15 |
| UPC | 33771 |
Compliance
NFA (National Firearms Act) compliance is crucial for legal ownership and transfer of regulated firearms and accessories like short-barreled rifles, suppressors, and certain types of ammunition, ensuring adherence to federal regulations to avoid legal penalties and ensure responsible firearm ownership.
Please select an FFL from the table below, if you do not see your desired FFL, click "Set Later" and you will be able to enter your FFL's information after checkout.
| Name | City | State | ZIP | Phone | |
|---|---|---|---|---|---|
|
Loading FFL contacts, please wait...
|





