20” 5.56 AR-15 Upper Receiver – 13” Heavy Duty Quad Rail

Built for durability, accuracy, and real-world performance, this 20-inch 5.56 AR-15 upper receiver is engineered for shooters who want maximum velocity, improved sight radius, and a rock-solid rail platform. Featuring a rifle-length gas system and Super heavy-duty 13” quad rail with ASAL™ anti-slip mounting technology, this upper is designed to stay locked in under recoil, heat, and hard use.

Every upper is professionally assembled, quality checked, and test-fit by experienced builders, then backed by our limited lifetime warranty.

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Key Features

• 20” 5.56 NATO 4150 CMV steel barrel
• Nitride-treated barrel for corrosion resistance and long service life
• 1:7 twist rate (optimized for heavier 5.56 bullet weights)
• Rifle-length gas system for smooth recoil impulse and reliability
• .750” steel gas block (dimpled barrel for secure alignment)
• Stainless steel rifle-length gas tube
• 13” super heavy-duty SHD quad rail handguard
• ASAL™ anti-slip / anti-lift mounting system for enhanced rigidity
• Anti-rotation tab rail interface for improved lockup
• 7075-T6 mil-spec forged upper receiver
• Type III hard coat anodized finish (black)
• M4 feed ramps
• Installed forward assist and dust cover
• A2 flash hider installed

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Built for Strength, Accuracy, and Control

This upper is built around a 20-inch barrel platform, delivering excellent velocity and long-range performance while maintaining the reliability expected from a rifle-length gas system. The nitride finish enhances wear resistance and makes cleaning easier after extended shooting sessions.

Paired with a 13” heavy-duty quad rail system, this upper provides maximum rigidity for optics, night vision, lasers, and vertical grip setups. The quad rail design remains one of the most stable mounting platforms available for shooters who prioritize durability over weight savings.

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ASAL™ Mounting System – Eliminates Handguard Movement

This upper features a 13” quad rail utilizing the ASAL™ anti-slip / anti-lift system, engineered to dramatically reduce handguard movement under recoil and thermal cycling.

Benefits include:

• Reduced rail lift and shift under firing stress
• Improved optic and laser zero retention
• Increased rigidity under hard use conditions
• More consistent point of impact over extended strings of fire

The result is a rail system that stays locked in place even under demanding conditions.

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Precision Barrel Assembly

The 20” barrel is professionally installed and secured with:

• Dimpled barrel for precise gas block alignment
• Proper torque and installation procedures
• Steel .750” gas block for durability and heat resistance
• Stainless steel gas tube for long-term reliability

This ensures consistent gas flow, reliable cycling, and long service life.

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Upper Receiver Specs

• 7075-T6 forged aluminum upper receiver
• Mil-spec Type III hard coat anodizing
• M4 feed ramps for reliable feeding
• Installed forward assist assembly
• Installed dust cover
• Fully assembled and inspected

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Ideal Applications

• Precision rifle builds
• Duty / defensive AR-15 setups
• Long-range 5.56 NATO platforms
• Suppressed or unsuppressed rifle systems
• Heavy-use training or professional environments

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Why Choose This Upper

Unlike standard lightweight carbines, this 20” platform is built for shooters who prioritize:

• Maximum ballistic performance from 5.56 NATO
• A stable, rigid quad rail mounting system
• Long-term durability under hard use
• Professional-grade assembly and inspection

Every upper is properly built by experienced technicians and backed by our Mid State Firearms limited lifetime warranty for confidence in the field.

Pro Tip: Add a Bolt Carrier Group to your order and we’ll test fire with that exact BCG to ensure it’s ready to go, right out of the box. No headache, just drop on your lower and head to the range.