The .300 AAC Blackout cartridge was engineered to deliver excellent performance from shorter barrels, making the 10.5-inch platform one of the most practical and capable AR-15 configurations available. Whether you’re shooting lightweight supersonic loads or heavy subsonic ammunition, a properly built 10.5″ upper offers exceptional versatility in a compact package.
Built around a premium 4150 Chrome Moly Vanadium barrel with a durable QPQ nitride finish, this upper is designed for dependable performance and long service life. The 1:8 twist rate is optimized to stabilize the full spectrum of common .300 Blackout projectiles, from lightweight hunting ammunition to heavy subsonic loads.
Combined with a pistol-length gas system and lightweight 9.7″ Rugged free-float M-LOK handguard, this upper provides smooth operation, excellent balance, and outstanding handling characteristics.
Optimized for the .300 Blackout Cartridge
Unlike cartridges that lose significant performance in short barrels, .300 Blackout was specifically designed to perform efficiently in compact platforms.
Advantages of the 10.5″ .300 Blackout platform include:
- Excellent energy from a short barrel
- Compact overall length for improved maneuverability
- Compatible with both supersonic and subsonic ammunition
- Ideal for suppressor-ready builds where legally applicable
- Reduced blast compared to similarly sized 5.56 platforms
- Outstanding versatility for hunting, range use, and defensive applications
For shooters seeking a compact AR with broad ammunition flexibility, few configurations are as capable as a quality 10.5″ .300 Blackout upper.
Premium Barrel Construction
This upper features a precision-manufactured barrel built from 4150 Chrome Moly Vanadium steel.
Barrel Specifications
- 10.5″ barrel length
- .300 AAC Blackout chamber
- 4150 CMV steel
- QPQ nitride finish
- 1:8 twist rate
- Pistol-length gas system
- 5/8×24 muzzle threads
The nitride finish increases surface hardness while providing excellent corrosion resistance and reduced wear for extended service life.
The 1:8 twist rate offers excellent stabilization across the wide range of bullet weights commonly used in .300 Blackout platforms.
9.7″ Rugged Free-Float M-LOK Rail
The included 9.7″ Rugged Rail combines lightweight construction with exceptional rigidity through its advanced wedge-lock attachment system.
Rather than relying on simple clamping pressure, the wedge-lock design distributes force evenly around the barrel nut, producing a secure interface that resists movement under demanding conditions.
Features include:
- Aircraft-grade 6061-T6 aluminum construction
- Reinforced wedge-lock mounting system
- Slim ergonomic profile
- Magpul-compatible M-LOK attachment slots
- Skeletonized design for reduced weight
- Large ventilation ports for improved barrel cooling
- Steel barrel nut
- Type III hard coat anodized finish
- Compatible with low-profile gas blocks
The 9.7-inch length provides excellent hand placement while maintaining ideal proportions for a 10.5-inch barrel.
Forged 7075-T6 Upper Receiver
Every upper starts with a forged 7075-T6 aluminum receiver finished with military-grade Type III hard coat anodizing.
Features include:
- Forged construction
- Black Type III anodized finish
- Forward assist installed
- Dust cover installed
- Standard AR-15 compatibility
Forged receivers remain the benchmark for durability and strength in the AR platform.
Reliable Pistol-Length Gas System
This upper utilizes a pistol-length gas system specifically suited to the .300 Blackout cartridge.
Components include:
- Steel low-profile gas block
- Stainless steel pistol-length gas tube
The shorter gas system helps ensure reliable cycling across a broad range of ammunition types, including many popular subsonic and supersonic loads when paired with an appropriate buffer system and quality components.
Outside Threaded 3-Prong Flash Hider
The included 3-prong flash hider is machined from nitrided 4140 steel and features external 13/16×16 threads for compatibility with Castle-style blast shields and forward blast diverters.
Key features include:
- Effective flash suppression
- Durable nitride finish
- Cone-style locking interface for improved concentricity
- 13/16×16 external threads for blast shield compatibility
- Crush washer included
This design allows shooters to add a compatible blast shield that redirects muzzle blast and concussion forward, improving shooter comfort in many applications.
Built by Mid State Firearms
Since 2014, Mid State Firearms has built a reputation for delivering dependable AR-15 components assembled with care and attention to detail.
Every upper is professionally assembled using quality components, proper torque procedures, and careful inspection throughout the build process.
When you purchase a bolt carrier group with your upper, the complete assembly is test fired using that exact bolt carrier group before shipment to verify proper function and compatibility.
This commitment to quality control helps ensure your upper arrives ready for reliable performance.
Technical Specifications
- Caliber: .300 AAC Blackout
- Barrel Length: 10.5″
- Barrel Material: 4150 CMV Steel
- Barrel Finish: QPQ Nitride
- Twist Rate: 1:8
- Gas System: Pistol Length
- Gas Block: Steel Low Profile
- Gas Tube: Stainless Steel
- Muzzle Threads: 5/8×24
- Flash Hider: 3-Prong Outside Threaded (13/16×16)
- Upper Receiver: Forged 7075-T6 Aluminum
- Upper Finish: Type III Hard Coat Anodized Black
- Handguard: 9.7″ Rugged Free Float M-LOK
- Handguard Material: 6061-T6 Aluminum
- Includes: Forward Assist and Dust Cover Installed
Frequently Asked Questions
Why is 10.5 inches a popular barrel length for .300 Blackout?
The .300 Blackout cartridge was specifically designed to perform efficiently from shorter barrels. A 10.5-inch barrel delivers excellent velocity and energy while providing a compact, easy-to-handle rifle configuration.
Can this upper shoot both subsonic and supersonic ammunition?
Yes. The 1:8 twist barrel is designed to stabilize a wide range of .300 Blackout bullet weights commonly found in both subsonic and supersonic factory ammunition.
What are the muzzle threads?
The barrel features industry-standard 5/8×24 threads, making it compatible with many .30 caliber muzzle devices, suppressor mounts, compensators, and flash hiders.
What advantages does the pistol-length gas system provide?
The pistol-length gas system is well suited to the .300 Blackout cartridge and is designed to promote reliable cycling across a broad range of ammunition while maintaining smooth operation.
Is the handguard free floated?
Yes. The 9.7″ Rugged Rail is a true free-float design that avoids contact with the barrel, helping preserve accuracy and consistency while providing ample room for accessories.
What makes the Rugged Rail different?
The Rugged Rail uses an advanced wedge-lock mounting system that applies even pressure around the barrel nut for exceptional rigidity and resistance to movement under heavy use. The lightweight skeletonized profile also promotes cooling while reducing overall weight.
What happens if I order a bolt carrier group with this upper?
When a bolt carrier group is purchased with this upper, Mid State Firearms installs and test fires the upper using that exact BCG before shipment to verify proper operation and compatibility.
Why buy from Mid State Firearms?
Since 2014, Mid State Firearms has specialized in AR-15 components and complete uppers built with quality materials and professional assembly practices. Every upper is carefully assembled, inspected, and backed by a commitment to reliability and customer satisfaction. Our unique test-fire process with qualifying bolt carrier group purchases provides an additional level of quality control that helps ensure dependable performance right out of the box.
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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.