CMMG 55BA457 BOLT ASSEMBLY AR15

The CMMG Bolt Assembly AR-15 (55BA457) is a replacement and spare bolt assembly for mil-spec AR-15 platforms chambered in 5.56x45mm NATO and .223 Rem, built from high-grade steel with a durable phosphate finish for builders, armorers, and shooters who need a reliable drop-in bolt solution. This AR-15 bolt assembly for 5.56 NATO and .223 Remington arrives pre-installed with ejector, extractor, and gas rings ready for immediate installation into any compatible bolt carrier group.

Key Features

• Part number: 55BA457
• Compatible calibers: 5.56x45mm NATO, .223 Rem, .300 BLK, .350 Legend
• Platform: AR-15, Mk4
• Bolt material: 9310 steel
• Bolt finish: Phosphate, black
• Extractor material: 4140 steel
• Extractor finish: Phosphate, black
• Pre-installed components: Ejector, extractor, gas rings
• Weight: 0.13 lbs
• Length: 3.00 inches
• Width: 0.75 inches
• Height: 0.75 inches
• Country of manufacture: United States
• Warranty: CMMG Lifetime Quality Guarantee

Special Features

• The 9310 steel bolt body is a high-nickel, case-hardened alloy selected specifically for bolt applications because it delivers superior toughness and fatigue resistance compared to the more common 158 tool steel used in lower-tier bolt assemblies.
• The 4140 steel extractor is a step up in tensile strength and wear resistance over standard carbon steel extractors, maintaining reliable case extraction across high-volume shooting and sustained use without accelerated wear at the claw.
• The phosphate finish on both the bolt body and extractor provides a matte, corrosion-resistant surface that holds lubrication effectively, reducing metal-on-metal friction during cycling and extending service intervals between cleanings.
• Arriving with the ejector, extractor, and gas rings already installed, this assembly drops directly into a compatible bolt carrier without requiring any staking, pressing, or assembly work beyond inserting it into the carrier.
• CMMG backs this bolt assembly with a Lifetime Quality Guarantee, covering the component against material and workmanship defects for the life of the product.

Practical Benefits

• Whether you are completing a new AR-15 build, refreshing a worn bolt, or stocking a spare for a range kit, the CMMG Bolt Assembly (55BA457) installs directly into any mil-spec bolt carrier without fitting or modification.
• The pre-installed ejector, extractor, and gas rings eliminate the bench work and small-parts handling that make bolt assembly a frustrating step for newer builders, getting your rifle back in service faster.
• Compatible with mil-spec AR-15 carriers across 5.56 NATO, .223 Rem, .300 BLK, and .350 Legend platforms, this bolt fits a broad range of the most common AR builds in use today.
• The combination of 9310 bolt steel and 4140 extractor steel matches or exceeds the material spec found in many factory-built rifles, making this a solid direct replacement that does not sacrifice quality for price.
• Ideal for armorers maintaining multiple rifles, competitive shooters keeping a spare bolt on hand at matches, and builders sourcing quality components for custom AR-15 projects.
• Your AR-15 gets a replacement bolt sourced from one of the most established AR-platform manufacturers in the industry, backed by a lifetime guarantee that protects your investment in the build.

The CMMG Bolt Assembly AR-15 (55BA457) for 5.56x45mm NATO and .223 Rem is a dependable option and proven platform component for the AR builder, armorer, or shooter who demands reliable, properly spec'd drop-in parts from a manufacturer with a lifetime quality guarantee behind every piece.