Colt's Manufacturing AR-15 / M4 Factory OEM Bolt Repair Kit - SPK403979
Product Description
The bolt carrier group (BCG) is the unyielding heart of any AR-15 or M4 rifle platform, enduring massive pressures, abrasive friction, and volatile thermal shocks with every squeeze of the trigger. Over thousands of live-fire cycles—particularly under modern suppressed operational conditions—the intense gas blowback and violent cycling rates introduce extreme stress to the bolt’s smallest mechanical sub-components. Gas rings erode and lose their sealing efficiency, extractor springs lose their structural elasticity, and high-velocity extractor pins degrade under continuous shearing forces. The Colt AR-15 / M4 Bolt Repair Kit eliminates these critical failure points, packaging an absolute factory-direct, mil-spec restoration group engineered to revive your primary firearm assembly without replacing the entire expensive bolt body.
Every single component in this 10-piece professional refresh kit is manufactured in the United States using identical military-tier metallurgical specifications and precision geometry that Colt implements on its duty-issue infantry rifles. The replacement extractor is forged from high-tensile carbon steel and protected by a dense, non-reflective manganese phosphate conversion coat to ward off aggressive carbon fouling and friction wear. Accompanied by three premium steel gas rings configured to establish a clean, gas-tight seal inside the carrier bore, this kit guarantees maximum pressure retention and clean cycling timing. From the heavy-duty extractor spring assembly to the indispensable firing pin retaining cotter pin, this factory kit eliminates the mechanical slack and loose tolerances frequently associated with budget-friendly aftermarket components.
In application, this field repair kit serves as vital workbench insurance for tactical armorers, competitive match shooters, and defensive-focused citizens alike. Instead of waiting for a broken extractor lip or flat gas rings to deadline a critical training course or field assignment, this kit allows you to perform complete preventative maintenance overhauls on your timeline. Seating each pin, plunger, and spring returns the bolt to its precise factory mechanical baseline, producing positive, aggressive casing extraction, smooth ejection trajectories, and absolute lockup uniformity. Keep this compact kit packed inside your primary range bag or armorer drawer to insulate your modern sporting rifle from unexpected down-time during hard tactical deployments.
*Armorer Bench Notes & Technical Maintenance Guidance: The Colt SPK403979 assembly is universally cross-compatible with standard mil-spec .223 Remington, 5.56x45mm NATO, and .300 AAC Blackout bolt carrier groups. When overhauling your bolt, always stagger the three split gaps of the new gas rings roughly 120 degrees apart around the bolt body; if the ring gaps line up perfectly inline, excessive drive gas will leak past the seals, inducing sluggish short-cycling malfunctions. To verify your gas ring health after installation, perform the vertical drop test: insert the assembled bolt into the clean carrier channel and stand the unit vertically on the bolt face on your bench. If the weight of the carrier causes it to slide downward over the bolt under its own mass, the gas rings are out of spec or worn; a healthy ring seal must support the full mass of the carrier. Apply a micro-drop of premium synthetic gun oil directly to the extractor pivot pin and extractor spring insert during final assembly to smooth out mechanical travel paths.
Key Features
- Genuine Colt Factory OEM: Sourced directly from Colt's production lines to match authentic mil-spec prints, tolerances, and metallurgical formulas.
- 10-Piece Restoration Matrix: Furnished with every single high-wear internal component required to completely rebuild a standard AR-15 or M4 extractor and ejector face.
- Manganese Phosphate Armor: Extractor and pins feature a heavy parkerized finish that enhances surface lubrication retention and completely blocks environmental corrosion.
- Premium Gas Tight Sealing: Includes three high-tensile steel gas rings engineered to eliminate blow-by and maximize operating gas pressure inside the carrier.
- Essential Emergency Insurance: Compact, lightweight package functions perfectly as an emergency "oops kit" or field repair set to eliminate rifle down-time at the range.
Product Specifications
- Brand: Colt's Manufacturing
- Model Line: Factory OEM Replacement Parts Group
- MPN/SKU: SPK403979
- UPC: 098289600448
- Firearm Platform: AR-15 / M4 / M16 Rifle Series
- Calber Fitment: 5.56x45mm NATO / .223 Remington / .300 AAC Blackout
- Kit Contents: 1x Forged Extractor, 3x Steel Gas Rings, 1x Ejector, 1x Ejector/Safety Detent Spring, 1x Extractor Spring Assembly, 1x Extractor Pin, 1x Ejector Roll Pin, 1x Firing Pin Retaining Pin
- Material Base: Heat-Treated Carbon Steel / Premium Music Wire Springs
- Finish Treatment: MIL-SPEC Manganese Phosphate / Matte Black Oxide
- Country of Origin: United States
Factory Colt repair kit for AR15/M4/M16 rifle bolts.
