Quality AR 15 uppers, AR15 parts, AR-15 rifle manufacturer. Friday Harbor, WA
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16" 300 Blackout Melonite w/ 10" SDX Mk II Rail Upper
Return To 300 Blackout AR15 Upper Assemblies | Proceed To Cart
Original Price $349.99
Your Price $249.99
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Looking for something compact, deadly accurate and small in the hand? Hardened Arms is pleased to bring you our first slim line style 10" SDX Mk II Slim Line MLok Rail. Featuring MLok attachment points at 3, 6 and 9 with a full length top rail you will love the new rail style. Matched with our 16" 4150CMV 300blk barrels machined in house this deal won't last long!


Complete AR15 SDX Mark II Upper Receiver Assembly:
  • Hardened Arms M4 Feed Ramp Flat Top Receiver
  • Black anodized mil-spec finished upper receiver
  • Feed ramps for increased feeding reliability on barrel and upper
  • Laser etched T-Marked upper receiver
  • 4150CMV .300 Blackout High End Barrel
  • Black Melonited/QPQ Finish
  • Stress Relieved for superior accuracy
  • Chambered in .300 Blackout
  • 16" HBAR Profile barrel with M4 Extension
  • .750" barrel diameter at gas block
  • 5/8x24 threaded muzzle/barrel
  • Low profile gas block
  • Barrel dimpled to secure gas block
  • Pistol length gas system
  • A2 flash hider
  • 10" SDX Mark II Slim Line MLok Rail (1.46" Cross Section, 1.3" Inner Diameter)

Fits any mil-spec AR15 lower receiver.

Hardened Arms uppers are high end, accurate, head spaced, inspected and test fired prior to shipping. They are built using stringent specs, top quality parts and procedures to ensure maximum reliability and performance. 

You are responsible for knowing your state laws regarding barrel lengths, pistol, Short barreled rife restrictions. 20% restocking fees if you can not take delivery due to state restriction. Dealer programs are available on our website. Two year warranty against manufacturer defects. Finishes will wear with use, no warranties apply to finish wear.
515 Tucker Ave, Friday Harbor, WA 98250 | sales@hardenedarms.com
Phone: 425-530-0837