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AR-15/M16/M4 5.56 Left Handed Full Auto Bolt Carrier Group – NiB-X Nickel Boron POLISHED

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Nickel boron makes surfaces harder, slicker and safer from corrosion. A polished nickel bolt carrier group brings those properties to the heart of your AR-15, giving it impressive reliability and enhanced function — plus an eye-catching appearance. WMD Guns treats our nickeled BCGs with our proprietary NiB-X® coating to give you the best of this top-tier protection.

Designed for the left-handed AR-15, M16 or M4, this bolt group features a full-auto configuration with greater rear mass to support proper timing in fully automatic or semi-automatic firearms. Every piece is made to exact government specifications for a long service life and a drop-in fit. Order now or explore additional information below to see what makes this piece an exceptional addition to any left-handed AR.

Availability: In Stock

SKU: NiBXBCG0001-LH Return Policy



Left-Handed Nickel Boron Full-Auto Bolt Group in 5.56

At WMD Guns, we specialize in firearm coatings and components that use them to their full advantage. This left-handed 5.56 bolt carrier group (BCG) is a perfect example of these specialized products. Sized for the AR-15, M16 and M4 and designed for left-eject firearms, this part is ready to deliver exceptional performance.

These polished nickel left-handed BCGs undergo application of our proprietary NiB-X® coating on every critical surface. The parts beneath that coating are all produced, machined and processed to U.S. government specifications to provide perfect fit and long-term longevity. Even when subjected to a grueling 30,000-round endurance test, this BCG refuses to fail.

Our full-auto 5.56 BCGs for left-handed ARs work perfectly for suppressed firearms, short-barreled rifles and other rigs that demand the best performance for specialized applications.

Why Buy a Nickeled BCG for Your AR-15?

Direct gas impingement is a dirty system. Your AR-15, M16 or M4 cycles by funneling the hot gases generated by powder burn from the barrel into the receiver, pushing your BCG rearward to eject a spent case, cock the hammer and reload the firearm. That means your bolt group is being exposed to carbon particles with every shot. 

Over time, that carbon builds up on the surfaces of your BCG, eventually affecting its movement and performance. On uncoated steel, removing it requires harsh solvents and scrubbing. With a nickel boron coating, however, your BCG will gain the exceptional lubricity of this protective material, allowing it to function much longer before cleaning and letting the user simply wipe carbon buildup away with a rag. 

A polished nickel BCG for your lefty AR is an excellent way to help make sure your firearm is ready to handle heavy use and stay reliable in any situation.

What Makes a Bolt Carrier Group Full Auto?

Dropping an M16 BCG into your left-handed AR won’t make the gun fully automatic unless you have a few other pieces to support that function. The name comes from this style of bolt carrier having additional material at the rear to interface with a full-auto trigger mechanism.

A semi-auto BCG is a little lighter since it excludes this extra mass, but both work well in civilian firearms. Some shooters prefer the full-auto design because the additional weight of the M16-style BCG lowers recoil and slightly slows the gun’s cycle time for greater reliability and decreased wear.

What You Get With Our Polished Nickel Left-Hand BCG

This polished silver BCG gives your .223/5.56 firearm some visual flair, plus top-end performance thanks to its premium materials and exacting production practices. We treat every component below with our NiB-X® coating to prepare it for use in any circumstance. 

  • Carrier: Case-hardened and nickel boron-coated 8620 material with full-auto lug. Ready to cycle in M16s, M4s and AR-15s. 
  • Bolt: Case-hardened 9310 steel subjected to shot peening and magnetic particle inspection. Includes Mil-Spec extractor, gas rings and ejector with NiB-X® coating, plus specialized O-ring buffer. 
  • Gas key: Hardened per USGI specifications. Placed using grade 8 fasteners, Permatex Sealing Compound and staking procedure per military guidelines.
  • Firing pin: Hardened, heat-treated and chromed per government instructions.
  • Cam pin: Manufactured and hardened as recommended in official drawings. Treated with NiB-X® coating for function and longevity.

You can buy a full-auto left-hand AR bolt without having to apply for a tax stamp or complete any paperwork with the ATF. What’s more, our NiB-X® coating features a lifetime guarantee

WMD Guns is proud to offer the high-performance nickel BCG your left-handed AR build deserves. Buy online here or contact our team with any questions or concerns about our products.

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