Group Shot
6 Critical Tips to Choosing the Right AR-15 Bolt Carrier Group (BCG) by Jason L. Grant
The Bolt Carrier Group (BCG) is the heart of the AR-15 weapon system, and there are many manufacturers of BCGs to choose from. When evaluating Bolt Carrier Groups, there are also many mechanical factors to consider, which are typically indicative of the quality of the machining and testing processes. The quality of BCGs can vary greatly between different manufacturers, but surprisingly the difference in price for this primary component only ranges between $10 to $40. So whether you’re doing a high-end or budget build, there’s no excuse not to utilize a quality BCG.
So you’re probably wondering, “What makes the difference in quality between different AR-15 BCGs?” In order to answer this question, you need to be able to properly evaluate the following factors:
- What quality steel is the BCG made of?
- Has the Bolt been shot peened?
- Is the Bolt Carrier chrome lined?
- Is the Gas Key properly staked?
- Has the BCG been HP and MPI Tested?
- Is the BCG an AR-15 or M16 model?
1. The Steel:
Make sure the BCG is made of a quality steel such as Carpenter No. 158 alloy, which is an exceedingly high strength, case hardening alloy mold steel. The metal is formed in cold-melt electric furnace process, manufactured to a narrow range of analysis limits. The process involves electric furnace melting under closely controlled conditions which assures unvarying uniformity.
2. Shot Peened Bolt:
The Bolt is the first part that can wear out on a BCG if the proper processes are not utilized. Only settle for a bolt that has been shot peened for extraordinary strength. Shot peening is a manufacturing process in which small steel balls are blown with com-pressed air against a metallic part to stress-relieve the external surface of a part. This process dramatically increases the fatigue life of the Bolt.
3. Chrome Lining:
Make sure the Carrier is chrome lined as this protects the steel from the highly erosive gas that enters the carrier, in addition to creating a slick surface for smooth operation. Most importantly, make sure that the gas key is chrome lined as this is where the greatest amount of erosive gas is found in a direct impingement (DI) system.
4. Gas Key Staking:
This is one of the most obvious tell-tale signs of a good or bad BCG. Gas keys cannot be mounted on the carrier using locktite or any other adhesive on the threads due to the fact that the temperatures experienced during weapon cycling will cause the locktite to fail. The mechanical process of staking punches metal into the carrier key screws. If this is not properly done, the keys will become loose and the AR becomes a single shot or worse as it can try to feed a live round with an empty still in the upper.
5. Magnetic Particle Inspection (MPI) & High Pressure Testing (HPT):
As a matter of quality control, make sure that the BCG is inspected and tested using MPI and HPT methods. MPI uses magnetic fields and small magnetic particles (i.e. iron fillings) to detect flaws in components. HPT is performed to make sure that the bolt can withstand pressures well above what is experienced during the most brutal field operations.
6. AR-15 vs. M16 BCG?:
Regardless of what you may have heard from some guy on an internet forum, I’m telling you for a fact, you can utilize an Full-Auto M16 BCG in a civilian legal semi-auto AR-15 rifle. An M16 (full auto) carrier will improve reliability by increasing “lock time” when cycling and slightly slow down the cyclic rate. The M16 carrier has less metal removed from its underside and is heavier than the AR-15 version by approximately 0.3 to 0.5 ounces. This helps reduce recoil and protect the firing pin since it is fully shrouded so that the hammer is cocked by the carrier and not the firing pin itself.
Some of the industry’s best BCGs are made by Daniel Defense, BCM, Colt and FailZero. But regardless of what BCG you choose, basing your choice on the factors mentioned above will likely ensure that the rest of your rifle will need replacing before your next BCG.
About the Author
Jason Grant has been a long-time rifle, pistol, and shotgun enthusiast as well as a 3 gun competition shooter for over 13 years. Jason’s primary sources of information consist of personal experience and information obtained from blacksuntactical.com, nra.org, and gunsandammo.com.
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January 10, 2012 8:34 am
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