Spike's Tactical ST5BG01 Bolt Carrier Group - .223 Rem/5.56x45mm NATO, Black Phosphate Steel, AR-15/M16 Full Auto

The Spike's Tactical ST5BG01 bolt carrier group is a matched mil-spec assembly purpose-built for .223 Remington and 5.56x45mm NATO AR-15, M16, and M4 platform rifles. Whether you're running a semi-auto build or working with a full-auto or burst-capable receiver, this carrier group delivers the reliability you need through precision machining and hardened components. The bolt and carrier are manufactured to military specification dimensions using modern quality-control processes, and the bolt undergoes magnetic particle inspection to catch any internal flaws that could compromise durability or cycling.

What sets this Spike's group apart is the attention to detail in the critical wear surfaces. The carrier features hard chrome plating on the interior and is machined with a full-length M16-type shroud on the underside—that shroud is the key that trips the auto sear in rifles configured for full-auto or burst fire. The extractor is tool steel, fully staked, and works in concert with a properly staked carrier key to ensure consistent, dependable rounds downrange. You'll also notice the laser-engraved Spike's Tactical logo on the carrier side, visible when you open the ejection port door—a small touch that marks quality craftsmanship.

The black phosphate finish is the mil-spec standard (MIL-STD-171 5.3.1.2), proven for corrosion resistance and durability in field conditions. This is a workhorse component for shooters who demand reliability, whether you're building an AR for hunting, tactical training, or precision rifle work. Spike's reputation in the AR community is built on this kind of no-nonsense engineering.

Key Features

• Mil-spec matched bolt and carrier set, precision-machined for reliability in semi-auto and full-auto rifles
• Hard-chromed interior carrier for durability and smooth function
• M16-type full-length auto sear shroud on carrier underside for full-auto/burst operation
• Bolt inspected via magnetic particle testing to ensure structural integrity
• Tool steel extractor, fully staked, for consistent extraction
• Fully staked carrier key for secure assembly and reliable cycling
• Black phosphate (mil-spec) finish for corrosion protection
• Laser-engraved Spike's Tactical logo on carrier

Specifications

Frequently Asked Questions

Will this bolt carrier group work in my AR-15 or M16?

Yes. The ST5BG01 is designed for .223 Remington and 5.56x45mm NATO and is compatible with standard AR-15, M16, and M4 platform rifles. The bolt and carrier are machined to mil-spec dimensions, so they'll function in any receiver spec'd for those calibers.

What's the difference between this carrier and a standard semi-auto carrier group?

This carrier is machined with a full-length M16-type shroud on the underside. That shroud is designed to trip the auto sear on rifles configured for full-auto or burst fire. In a standard semi-auto receiver, the shroud is simply a non-functional feature; it won't affect reliability or function. The hard-chromed interior and magnetic particle inspected bolt are premium touches across the board.

Is the bolt inspected for defects?

Yes. Every bolt is magnetic particle inspected to catch any internal flaws that could compromise structural integrity or cause premature failure. This is a critical quality-control step that catches issues invisible to the naked eye.

What does the black phosphate finish protect against?

Black phosphate is the mil-spec standard finish for AR-15 and M16 components. It provides reliable corrosion resistance in field conditions and is durable under normal use and maintenance. The hard-chromed interior of the carrier adds another layer of durability where friction is highest.