Brownells M16 Bolt Carrier Group, Mpi Inspected, C158 Steel, Po4

The Brownells M16 Bolt Carrier Group is a fully assembled, inspected component built to mil-spec standards for AR-15 and M16 platforms. Whether you're assembling a rifle from the ground up, replacing a worn carrier, or building a spare upper, this is the kind of no-nonsense part that keeps things running when it matters. Every bolt is Magnetic Particle Inspected (MPI) to catch internal flaws invisible to the naked eye—a quality check that tells you Brownells takes their reputation seriously.

Built from Carpenter C158 steel for the bolt and 8620 steel for the carrier, both materials are heat-treated and shot-peened to withstand repeated firing cycles. The carrier is chrome-lined inside, and both the bolt and carrier wear a durable matte black phosphate finish that resists corrosion without the tactical flash. The gas key arrives properly torqued and staked, and the extractor comes equipped with a red o-ring and spring—details that reflect mil-spec assembly standards rather than bare-bones cost-cutting.

This group will function in both semi-auto and full-auto platforms, making it a versatile choice for shooters who need a reliable, inspected carrier that doesn't come with surprises. If you're upgrading a rifle, building a new upper, or simply want a known-good spare in the safe, Brownells' quality control and straight-forward design make this an easy call.

Key Features

• Fully assembled and ready to install—includes bolt, carrier, gas key, firing pin, cam pin, and firing pin retaining pin
• Every bolt inspected via Magnetic Particle Inspection (MPI) for internal defects
• Carpenter C158 steel bolt, heat-treated and shot-peened for durability
• 8620 steel carrier, hardened and chrome-lined inside for longevity
• Gas key screws properly torqued and staked to prevent loosening
• Extractor fitted with red o-ring and spring
• Matte black phosphate finish resists corrosion
• Compatible with AR-15 and M16 rifles, semi-auto and full-auto platforms

Specifications

Frequently Asked Questions

Will this bolt carrier group work in my AR-15?

Yes. This M16 bolt carrier group is fully compatible with both AR-15 and M16 platforms, functioning in both semi-auto and full-auto rifles.

What does MPI inspection mean, and why does it matter?

Magnetic Particle Inspection detects internal flaws and stress cracks in the bolt that are impossible to spot with your eyes. Every bolt in this group is MPI'd before leaving Brownells, ensuring you're not installing a hidden defect that could fail under pressure.

Is the gas key pre-installed and staked?

Yes. The gas key arrives installed, properly torqued, and staked—meaning it's ready to go without additional work on your part.

What's included in this carrier group?

The group is fully assembled and includes the bolt, bolt carrier, gas key, firing pin, cam pin, firing pin retaining pin, and an extractor fitted with a red o-ring and spring.