The Undertow 16 inch upper build kit delivers a 5.56 NATO setup built around a 16 inch cold hammer forged M4 profile barrel with 1:7 twist and carbine length gas system. The 15 inch freefloat M Lok handguard provides modular mounting surfaces while maintaining a lightweight profile. This upper build kit includes the upper assembly with barrel and handguard. BCG and charging handle are not included.
The 16 inch barrel features cold hammer forged construction from 4150 CrMoV steel. Cold hammer forging compresses the steel during manufacturing, creating a denser grain structure that enhances strength and accuracy potential. The M4 profile provides appropriate rigidity while balancing weight. Parkerized finish provides corrosion resistance and durability. The 1:7 twist rate stabilizes a wide range of projectile weights from 55 to 77 grains effectively. Carbine length gas system provides reliable cycling across varied ammunition types.
The 15 inch freefloat M Lok handguard extends nearly to the muzzle device, maximizing usable mounting length. M Lok slots allow modular accessory attachment while maintaining a slim profile. Aluminum construction keeps weight manageable. The freefloat design eliminates contact with the barrel for improved accuracy potential. The 15 inch length provides ample rail space for lights, grips, and other accessories.
The upper receiver features M4 feed ramps machined into the receiver extension. These extended feed ramps guide cartridges smoothly from the magazine into the chamber, reducing feeding issues with varied ammunition types. M4 feed ramps are standard on modern AR-15 platforms and ensure compatibility with most barrels and bolts.
The carbine length gas system on a 16 inch barrel provides reliable cycling with standard 5.56 NATO ammunition. Carbine length gas systems deliver consistent function across varied ammunition types and environmental conditions. Micro low profile gas block keeps the sight plane clean under the handguard.
This upper build kit includes the upper assembly with barrel and handguard. BCG and charging handle are not included. The upper receiver is constructed from 7075 T6 aluminum with anodized finish for corrosion resistance and durability. The cold hammer forged barrel provides a solid foundation for accurate shooting.
Follow safe handling and manufacturer instructions. BCG and charging handle are not included. Ensure compatibility with your bolt carrier group and charging handle. Ensure compliance with all applicable laws.
Caliber: 5.56x45mm NATO
Barrel: 5.56 NATO 16” Barrel, Parkerized, Cold Hammer Forged, M4 Profile, 1:7 Twist, Carbine-Length Gas System
Barrel Length: 16 inches
Barrel Material: 4150 CrMoV
Barrel Twist Rate: 1:7
Barrel Finish: Parkerized
Barrel Profile: M4
Barrel Thread Pitch: 1/2x28
Barrel Gas System Length: Carbine
Upper Receiver: AR-15 Upper Receiver, M4 Feed ramps, 7075 T6 Aluminum, Anodized
Upper Receiver Material: 7075 T6 Aluminum
Upper Receiver Finish: Anodized
Handguard Style: M-LOK Freefloat
Handguard Length: 15 inches
Handguard Material: Aluminum
Gas Block: Micro Low-Profile Gas Block, .750 O.D Barrel Steel
Gas Block Size: 0.750
Muzzle Device Details: AR-15 1/2x28 TPI GI Birdcage Flash Hider 5.56 .223 A2
Muzzle Thread Pitch: 1/2x28
Color: Black
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