The AR-15 bolt carrier group (AKA the BCG) is the part of the rifle or pistol that is responsible for performing semi-automatic fire when the trigger is pulled. It does this by first allowing the firing pin to strike the primer on the chambered round. Then grabs and ejects the spent shell casing from the fired round. It then re-cocks the hammer in the lower receiver for the next round which ends up grabbing a new round from the magazine and chambering it.

Carpenter No. 158 steel is the mil-spec steel used for fabricating the bolt itself. This type of steel provides the best performance and lifespan for the BCG. C158 is case- (or surface-) hardened. This means the exterior of the steel is made to be very hard, preventing cracking and surface wear. Inside, the steel is softer and more flexible, preventing deformation and stress fractures.

These are two types of testing we do on all of our Bolt Carrier Groups.

HPT or High Pressure Testing, is another test performed by firing a high-pressure cartridge through the BCG being tested. HPT is done first to expose any potential flaws in the bolt. Then MPI testing is done to find any flaws or potential flaws.

MPI or Magnetic Particle Inspected, is a testing method used to test for microscopic cracks or fissures created during the manufacturing process. To test for this, the BCG is placed inside a magnetic field and a liquid solution containing magnetic particles is then applied to the steel. The magnetic particles will stick to any cracks, fissures, or tiny imperfections that are on or just under the surface. If any cracks, fissures or imperfections are found that BCG is scrapped.

Since the gas key wears out before any other components, the key is made as a separate component and bolts to the body of the carrier. To ensure the key doesn’t get loose after being subjected to gas and recoil, SIONICS BCGs are hand staked utilizing a Michiguns MOMOAKS staking jig. Staking the key in the MOMOAKS creates a much more consistent stake, which enhances the longevity of the bond created by the fasteners.

Of course.

Phosphate coatings are porous and absorb oil and lubrication well by design. These are current Mil-Spec by the U.S. Military. When used in conjunction with quality external oils, a phosphate coating will protect the external of the BCG from corrosion. But, you must lubricate phosphate finishes regularly to give that protection.

NP3 is an Electroless Nickel coating with embedded TEFLON. The TEFLON is bonded to the particles of Nickel at the molecular level providing self lubrication throughout the entire coating. The Nickel in this finish provides corrosion and abrasion resistance. NP3 BCGs require less lubrication and they typically withstand heat and friction better than a standard phosphate or nitride-coated BCG. Because NP3 is chrome-like, it wipes off and cleans easily, often requiring no solvents or harsh chemicals.

Shot peening is a process used to make metals more stress-resistant. It is commonly used in engine pistons. However, it is also used to make the SIONICS bolt carrier groups more durable and long-lasting.

We choose to use the OCKS (Optimized Carrier Key Screws) because of their unique design features. There are twelve splines on the heads, giving depressions and projections for carrier key metal to stake/flow into and engage like gear teeth. This makes sure we’ve got the best possible retention of carrier key screws.

Sprinco AR-15 Extractor Springs are made from high quality Chrome Silicon wire stock that has been heat treated, stress relieved, and cryogenically processed to produce long lasting durability. 5-Coil springs provide a higher spring pressure than OEM springs for use in all AR-15 pattern rifles and performs well even if the rifle is dirty.

Here at SIONICS, we test fire EVERY BCG, upper receiver group, and firearm.

Our test firing process is simple:

• BCGs get 5 rounds of M193 and another single round in a separate magazine to ensure function, ejection pattern, and lock-back.
• All upper receiver groups and firearms get 7 rounds of M193 and another single round in a separate magazine to ensure function, ejection pattern, and lock-back.