M16 vs AR15 BCG [Subtle Details Explained]

The Bolt Carrier Group (BCG) is often referred to as the heart of any AR-style rifle. It's a crucial component that interacts directly with the rounds fired, striking the primer, ejecting the spent casing, and chambering a fresh round.

When it comes to BCGs, there are two main categories: AR-15 BCGs and M16 BCGs. Here's a comprehensive look at the differences between the two.

AR-15 BCG (Semi-Auto BCG)

  • Design: The AR-15 BCG is designed for civilian use and is considered the civilian variant of the rifle.
  • Full Auto Capability: It lacks the full auto capability, meaning it can only shoot in semi-automatic fire.
  • Weight: It's lighter than the M16 BCG due to the absence of a full auto lug.
  • Availability: AR-15 BCGs are rare these days and can be more difficult to find.
  • Compatibility: It's not compatible with the M16 lower parts kit and cannot support selective fire capability.
  • Legal Aspects: It's legal for civilian use.

M16 BCG (Full Auto BCG)

  • Design: The M16 BCG is designed to work in both M16s and AR15s and is the most common form of BCG on the market.
  • Full Auto Capability: It has a full auto lug that facilitates cycling during selective fire with the correct timing, making it possible to shoot in full automatic fire.
  • Weight: It's heavier than the AR-15 BCG due to the presence of the full auto lug.
  • Availability: M16 BCGs are widely available and are considered the industry standard.
  • Compatibility: It's fully compatible with AR-15 lowers and AR-15 lower parts kits but not the other way around.
  • Legal Aspects: Though full auto firearms are regulated, the M16 BCG itself does not fall under these regulations, making it legal to purchase.

Key Differences

  • Full Auto Lug: The main difference lies in the presence of a full auto lug in the M16 BCG. This lug contacts the sear release in full auto trigger groups, allowing the gun to fire in fully automatic mode. The AR-15 BCG does not have this lug.
  • Weight: The absence of the full auto lug in the AR-15 BCG results in a lighter weight.
  • Compatibility: While the M16 BCG can work in both AR-15 and M16, the AR-15 BCG cannot support the full auto M16 lower parts kit.

Additional Considerations

  • BCG Coatings/Finishes: Various BCG coatings and finishes are available, such as Shot Peening, Magnesium Phosphate/Chrome (Parkerized), Black Nitride, and Physical Vapor Deposition (PVD), each with unique properties and applications.
  • Best BCG Brands: Brands like Toolcraft offer a variety of BCGs with top-notch machining quality, and Lewis Machine and Tool are known for high-end bolt carrier groups.
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