The AR57 ULT Upper Assembly 12" Barrel 5.7x28 ULT12 is a high-performance, complete upper receiver assembly designed to convert standard AR-15 lower receivers into a 5.7x28mm platform. This innovative upper allows shooters to enjoy the high-velocity, low-recoil benefits of the 5.7x28mm cartridge in a familiar AR-15 platform. Featuring a 12-inch barrel and a unique top-mounted magazine system compatible with FN P90 magazines, the AR57 ULT12 offers exceptional performance for sport shooting, training, and tactical applications.
Why Choose the AR57 ULT Upper Assembly 5.7x28?
The AR57 ULT Upper Assembly stands out as one of the most innovative ways to bring 5.7x28mm capability to the AR platform. Instead of requiring a completely new firearm, this upper assembly lets you use your existing AR-15 lower receiver, trigger group, and stock. The 12-inch barrel provides an excellent balance between velocity, maneuverability, and overall length. The ULT (Upper with Linear Top) design feeds ammunition from FN P90-style magazines mounted on top of the receiver, resulting in a compact and well-balanced firearm. This configuration delivers the high speed and flat trajectory of the 5.7x28mm cartridge while maintaining the ergonomics and modularity that AR-15 users love.
Key Features of the AR57 ULT12 5.7x28 Upper Assembly
- 5.7x28mm Chambering – High-velocity, low-recoil cartridge with excellent ballistic performance
- 12-Inch Barrel – Optimized length for increased velocity while maintaining a compact profile
- P90 Magazine Compatible – Uses standard FN P90 50-round magazines mounted on top
- Complete Upper Assembly – Includes barrel, bolt carrier group, handguard, and charging handle
- AR-15 Lower Compatible – Works with standard AR-15 lower receivers
- Lightweight Design – Well-balanced for fast handling and reduced fatigue
- Model ULT12 – Official AR57 part number
Performance and Build Quality
The AR57 ULT Upper Assembly is manufactured with precision components to ensure reliable function and accuracy. The 12-inch barrel is designed to maximize the velocity potential of the 5.7x28mm cartridge while keeping the overall length manageable. The unique top-mounted magazine system provides a low profile and excellent balance, making the firearm easy to maneuver in tight spaces. The bolt carrier group is specifically engineered for the 5.7x28mm round, delivering smooth and consistent cycling. AR57 has built a reputation for producing high-quality, innovative upper assemblies that allow shooters to explore different calibers on the AR platform without purchasing an entirely new rifle. The ULT12 model is particularly popular among enthusiasts who want the speed and capacity of the 5.7x28mm in a familiar ergonomic package.
Technical Specifications
| Product Name | AR57 ULT Upper Assembly |
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| Model Number | ULT12 |
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| UPC | 051497388553 |
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| Caliber | 5.7x28mm |
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| Barrel Length | 12 inches |
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| Magazine Type | FN P90 Style (Top Mount) |
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| Compatibility | Standard AR-15 Lower Receivers |
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| Product Type | Complete Upper Receiver Assembly |
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| Key Feature | 5.7x28mm AR Upper with P90 Magazine Feed |
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| Best For | Recreational Shooting, Training, Tactical Use |
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Transform your AR-15 into a 5.7x28mm platform.
The AR57 ULT12 Upper Assembly delivers high-velocity performance and P90 magazine compatibility in a compact 12-inch configuration.
Important Notice: This product is a firearm component and is subject to all applicable federal, state, and local laws regarding firearm ownership and assembly. The buyer is solely responsible for ensuring compliance with all laws in their jurisdiction. This product is intended for lawful use only by individuals legally allowed to possess and assemble firearms. Always follow proper firearm safety rules and manufacturer instructions. Keep out of reach of children. This product is intended for lawful use only.
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