MidState Defense 12.5″ AR-15 Barrel — 4150 CMV, Nitride (5.56 NATO)
Product by MidState Defense — available at Mid State Firearms
The MidState Defense 12.5″ AR-15 barrel is engineered for compact patrol, RECCE, and short-barrel builds where reliability and real-world performance matter. Machined from premium 4150 Chrome Moly Vanadium (CMV) and finished with a durable nitride treatment, this barrel includes M4 feed ramps, a carbine gas system, .750″ gas journal dimpled for gas block set screws, and 1/2-28 muzzle threads — everything a serious builder needs for a dependable, service-grade upper.
Key Features
- Manufacturer / Brand: MidState Defense
- Length: 12.5″
- Material: 4150 Chrome Moly Vanadium (CMV)
- Finish: Nitride
- Chamber / Caliber: 5.56 NATO (.223 compatible)
- Twist Rate / Spec: 1/8 (per manufacturer spec)
- Gas System: Carbine length
- Gas Journal: .750″ — dimpled for set-screw gas blocks
- Muzzle Threads: 1/2-28
- Feed Ramps: M4 style — guaranteed compatibility with Mil-Spec bolt carriers
- Application: Ideal for duty, RECCE, short patrol, or compact defensive uppers
Why Builders Choose MidState Defense
MidState Defense focuses on purpose-built barrels and components. The 12.5″ platform is tuned for correct dwell times and gas port sizing to improve reliability across suppressed and unsuppressed use. Finished with nitride for enhanced wear and corrosion resistance and built on a 4150 CMV blank, this barrel is a solid choice when you’re assembling a compact, serviceable AR-15 upper.
Compatibility & Build Notes
- Designed to fit standard AR-15 barrel nuts and .750″ gas blocks (dimpled for secure set-screw installation).
- Use with carbine-length gas tubes and standard 1/2-28 muzzle devices.
- Recommended: Have a qualified gunsmith perform final assembly and headspace verification if you are not experienced with upper builds.
- Always verify NFA/local laws before building short-barrel rifles (SBR) or pistol builds.
Pair With These Mid State Firearms Components
- Browse 5.56 / .223 barrels
- .750″ Gas blocks & mounting hardware
- Compatible handguards & accessories
- Questions? Contact Mid State Firearms
Quick Specs
| Platform | Ar15 / m4 |
| Barrel Length | 12.5″ |
| Material | 4150 CMV |
| Finish | Nitride |
| Caliber / Chamber | 5.56 NATO (.223 compatible) |
| Twist | 1/8 (as specified) |
| Gas System | Carbine |
| Gas Journal | .750″ (dimpled for set-screw gas blocks) |
| Muzzle Threads | 1/2-28 |
| Feed Ramps | M4 style |
Note: Specs shown reflect the manufacturer’s published details. If you need confirmation on any spec prior to purchase, contact Mid State Firearms — we’re happy to help with fitment and build guidance.
sound of freedom – This was a great set up. I loved being able to customize the set up. Only issue I had was my own fault as a newb to building these. I used a heavy barrel in a slim hand guard. It makes adding attachments tough with clearances. Hoping someday to also get an AR10 from here.