The Geissele® M4A1 Bolt Carrier Group is by far one of the best bolt carrier groups on the market. The fit and finish on these are always top notch. They are also manufactured to the stringiest Mil-Spec standards.
"Sourced from a Tier 1 supplier of the M4A1 carbine, this 5.56mm complete bolt carrier group is manufactured to the stringiest of military standards. Being off the same production line as bolt carrier groups found in carbines throughout the entire Department of Defense, these components are both high quality and highly reliable. The bolt carrier is manufactured out of 8620 steel with a chrome lined gas key and bolt recess in accordance with MIL-spec standards, and the bolts are produced out of Carpenter 158 also in accordance with MIL-spec standards. The gas keys are all properly torqued and staked, again in accordance with MIL-spec standards. All bolts have been high pressure tested (HPT) and mag particle inspected (MPI), exceeding the MIL-spec standard. Geissele also utilizes the latest revision extractor spring, O-ring and insert, which maximizes the reliability of the bolt carrier group. This ensures positive ignition and extraction of all types of ammunition, including military surplus ammunition known to have hardened primers." - Geissele Automatics®
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