12.5″ Rosco AR-15 Barrel — 4150 CMV, Nitride Finish, 1:7 Twist (5.56 NATO)

Overview
This 12.5″ Rosco barrel bridges the gap between SBR/pistol and RECCE platforms — a compact, precision-oriented barrel designed for modern carbine and patrol builds. Engineered with performance in mind, Rosco selects the proper twist rates, gas port diameters, and premium 4150 Chrome Moly Vanadium (CMV) steel for each model rather than using a one-size-fits-all approach. Finished with durable nitride treatment and factory-spec feed ramps, this barrel delivers consistent accuracy and reliable gas timing whether running suppressed or unsuppressed.

Why Rosco for an Intermediate Patrol / SBR Build?

Rosco barrels are developed with input from experienced consumers and military end users to produce a product tuned for real-world performance. The 12.5″ length gives you the maneuverability of a short-barrel platform while maintaining superior dwell timing and reliability for carbine gas systems. That makes this barrel ideal for operators building a compact patrol rifle, RECCE platform, or SBR/pistol upper (observe all NFA/local laws).

Key Features

• Barrel Length: 12.5″
• Barrel Material: 4150 Chrome Moly Vanadium (CMV)
• Finish: Nitride (barrel & extension)
• Caliber / Chamber: 5.56 NATO (shoots .223)
• Profile: Government (sturdy, service-grade contour)
• Twist Rate: 1:7 — optimized for heavier 5.56 loads and match bullets
• Gas System Length: Carbine length — tuned for reliable cycling
• Gas Journal Diameter: .750″ (fits standard .750″ gas blocks)
• Muzzle Threads: 1/2-28
• Barrel Crown: 11°
• Barrel Weight: 21.79 oz
• Manufacture: Rosco (OEM) — engineered for modern carbine shooters

Application & Notes

• Designed to perform well in compact duty and intermediate patrol platforms, RECCE builds, and short-barrel pistol uppers.
• Engineered with appropriate gas port sizing and dwell time for suppressed and unsuppressed use.
• Always verify headspace and fitment with a qualified gunsmith during installation.
• Check federal, state and local laws before completing an SBR or pistol build.

Specifications (Quick Reference)

Complete Your Build

Pair this Rosco barrel with a quality .750″ gas block, carbine gas tube, and a compatible muzzle device. Explore Mid State Firearms’ handguards, gas blocks, and upper parts to complete your upper receiver assembly:

• Browse AR-15 barrels (5.56 / .223)
• .750″ gas blocks & accessories
• AR-15 barrel selection & build guide

Questions? Contact Mid State Firearms for fitment guidance and build recommendations — Contact Us.