Green Mountain 5.56 AR-15 Barrel 11.5" M4 Finned Phosphate - GM-M11S

Upgrade your AR-15 build with the Green Mountain 5.56 AR-15 Barrel 11.5″ M4 Finned Phosphate. This precision-engineered barrel delivers reliable performance in a compact package, ideal for short-barreled rifles, pistols, or specialized tactical configurations. Manufactured by Green Mountain Rifle Barrel Co., a trusted name in mil-spec barrels, it combines rugged construction with features designed for accuracy, durability, and effective heat management during sustained fire.

Key Features

• Chrome-lined bore and chamber for superior corrosion resistance, reduced fouling, and extended service life even under demanding conditions.
• Phosphate exterior finish provides a durable, non-reflective coating that enhances protection against the elements while maintaining a professional tactical appearance.
• M4 finned profile promotes efficient heat dissipation, helping maintain barrel integrity and accuracy during rapid or prolonged shooting sessions.
• 1:7 twist rate stabilizes a wide range of 5.56 NATO and .223 Remington projectiles, including heavier match-grade ammunition for improved long-range performance.
• Carbine-length gas system with 0.75″ journal ensures smooth, reliable cycling in short configurations while supporting standard low-profile gas blocks.

Technical Specifications

• Barrel Length: 11.5 inches
• Cartridge Compatibility: 5.56 NATO / .223 Remington
• Platform: AR-15
• Twist Rate: 1:7
• Muzzle Thread Pattern: 1/2×28
• Gas System: Carbine
• Finish: Phosphate with chrome-lined bore and chamber
• Weight: 27.2 ounces

Benefits for Your Build

This barrel addresses common challenges faced by builders of compact AR platforms. The finned design helps mitigate excessive heat buildup that can affect accuracy in short barrels, while the chrome lining simplifies maintenance and resists wear from high-volume use. Its M4-style extension supports reliable feeding with standard AR-15 upper receivers, making it a dependable choice for defensive, training, or competition setups where consistency matters.

Whether you’re assembling a lightweight pistol build or restoring a classic M4-style configuration, this Green Mountain barrel provides the precision and toughness needed for serious applications without unnecessary bulk.

Why Choose Green Mountain?

Green Mountain Rifle Barrel Co. has built a reputation for producing high-quality, mil-spec barrels favored by enthusiasts and professionals alike. Each barrel undergoes rigorous manufacturing standards to ensure concentricity, proper headspacing, and consistent performance straight out of the box.