Geissele Automatics M4A1 5.56 Bolt Carrier Group

Manufactured by Geissele Automatics
SKU: 04-333
MPN: 04-333
Manufactured by Geissele Automatics
5 Reviews

Out of Stock

NOTE: Limit 1 per household. Quantities exceeding 1 will not allow checkout.



The bolt carrier group is an important component of any rifle or build, so why would you get something less than the best? The Geissele Automatics M4A1 bolt carrier group is built by a Tier 1 supplier for the Department of Defense and built on the same line as BCGs in use by the military. The full mass M16/M4 style bolt carrier is machined from proper 8620 tool steel with a chrome lined bore and properly staked, chrome lined gas key that will last a lifetime. Cut from Carpenter 158 steel, every single bolt assembly is magnetic particle inspected and high-pressure tested to ensure it is defect free. For optimum function, Geissele is utilizing the latest revision extractor spring, o-ring, and insert to ensure reliable extraction with all types of ammunition.

  • For 5.56 NATO / .223 Rem
  • High Pressure Tested
  • Magnetic Particle Inspected
  • Chrome lined bore and gas key
  • Properly staked gas key
  • Extractor O-Ring and Insert

Geissele Automatics manufactures confidence, offering quality triggers and components for the warfighter and competitor. They were established in 2004 with the mission to build the highest quality, reliable triggers for competition and their first trigger, the Hi-Speed National Match trigger, was so popular that they were asked by the Department of Defense to produce a select-fire trigger for the United States Special Operations. Again, it was a success and Geissele decided to bring a semi-automatic version to the civilian market for law enforcement and personal protection.
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Bolt FinishManganese Phosphate
Bolt MaterialCarpenter 158 Steel
BrandGeissele Automatics
Caliber Gauge5.56 NATO
Carrier FinishManganese Phosphate
Carrier Material8620 Carpenter Steel
Carrier StyleM16 Bolt Carrier
High Pressure TestedHigh Pressure Tested
Magnetic Particle InspectMagnetic Particle Inspected

Ratings & Reviews

5 reviews

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Works perfect


Worked great for my build. Had zero problems so far

Beautifully Crafted

by -

Excellent quality and performance. Beautifully crafted.

Start your next build with this


Amazing performance overall BCG is machined incredibly, properly staked gas key and no imperfections spotted & seems to be made to last forever

Great all around BCG


I used this BCG to finish up my Mk12 Mod 1 build; so far its been great with no reported issues. Tolerances & dimensions seem spot on and to be fairly gas efficient. Overall its a great buy, especially when they're on sale.

loving it


I bought this for my A.R pistol because of a little problem with the pistol. Cleaned and lubed my gun and it ran great in my pistol. Loving it!