The Bolt Carrier Group (BCG) is easily considered the heart of the AR platform. Rightfully so, considering the BCG is responsible for a large portion of the rifle's function. This guide will go over some Entry level, Mid Tier, and High Tier options for BCGs and some recommendations/considerations for purchasing a custom BCG.
(Disclaimer: These are all products that we have personally used and trust. If you are running a different setup, with good luck, we do not discount it.)
Both of these BCGs are the same make and follow the same specifications. Both of these BCGs are affordable and work really well for most people.
The carrier has a Black Nitride Finish, which provides some exterior lubricity. They both come with a properly staked Gas Key, which is extremely important for a BCG. Without a properly staked Gas Key, the gas that forces the carrier back will bleed off, causing the carrier to move at a slower speed, which can result in unreliability.
This Bolt Carrier is a great option for those who want something durable, and that has been quality checked thoroughly. This BCG is nothing fancy, gets the job done, follows Mil-Spec quality/guidelines, and comes at a reasonable price.
The LMT Enhanced BCG has a unique bolt and carrier.
The Carrier has an Altered cam path for longer dwell time and more robust extraction. Additional gas ports on the right side and modified orientation improve gas flowing through the ejection port and not into your face. Relief grooves added to the top and bottom to channel debris and maintain fluid movement.
The Bolt utilizes modified locking lugs that provide flexibility and durability in high-pressure, over-gassed loads. It also contains a “Lobster tail” extractor, which utilizes two springs that supposedly allow stronger and more consistent extraction with drastically improved spring life.
This BCG is not like any. Its "long-stroke design" delivers 60% more travel beyond the magazine, increasing magazine feed time and reducing the chance of bolt-over-base malfunctions. It also increases reliability when shooting suppressed/unsuppressed by delaying the unlocking of the bolt during the firing sequence, which allows the expanding gases more time to exit the bore, resulting in a reduction of back-pressure gases exiting the upper receiver group, and a softer felt recoil. This BCG is not inexpensive, but it does come as a kit with a proprietary spring and buffer.
The High Tier BCG's that are mentioned are not necessary. We typically recommend just doing a not-so-fancy BCM BCG.
Building out a Custom Bolt Carrier Group
Manufacturers We Recommend:
Microbest - Is well known for strict QC and very efficient gas sealing.
Schmid Tool - Is well known for triggers; they make most of the OEM triggers out there and offer BCGs.
Toolcraft - Is well known for a good generic BCG with lots of options.
- For the gas key, we recommend a hard chrome inner lining with a phosphate coating, 4130 steel.
- Michigun OCKS gas key bolts with the Scionics staking method. These are least likely to come loose under auto fire and heavy use.
- A sealing compound should be used on the mating surfaces as a secondary seal. We only know of Colt, LMT, and KAC doing this extra step to ensure a secondary gas seal for key bolt failures.
- We would suggest an NP3, nitride, or hard chrome bolt (C158 or similar steel) for ease of cleaning and added lubricity in the barrel extension.
- A beveled shoulder ejector (S7 steel) with Sprinco ejector spring.
- The extractor should be phosphate; this gives it grip on the casing and 4340 steel, but we would also recommend polishing the forward-facing lip to aid the casing slipping into the locking tooth (minor mod gunsmiths will make, pretty rare on OEM bolts). Sprinco 5-Coil extractor spring eliminates the need for the rubber donut or the black insert.
Here we would suggest two different avenues, one budget-minded and one not so much. Both can make a lasered logo, and I would do “full mass” auto carriers.
Non-budget - full hard chrome bolt carrier out of 8620 steel.
Budget - Black nitride 8620. For us, this is more desirable than chrome-lined because I believe you can only have a phosphate outer coating, which can gum up and be hard to clean. Hard chrome is a tip of the hat to the original m16 carriers and not flashy like NP3. However, NP3 could be a third option.
Firing Pin/Retainer/Cam Pin/Rings:
We would suggest an 8740 steel, hard chrome firing pin. 1038 steel retaining pin that is phosphate coated and a 4340 NP3 coated cam pin—Mil-Spec stainless gas rings.