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The bolt carrier group is the beating heart of any AR-15, and this is not the place to cut corners. The Spikes Tactical ST5BG01 is a complete, drop-in M16-cut BCG that arrives fully assembled and tested, so all you do is slide it into your upper and get to work. It runs the full-auto profile carrier, which adds a little mass over a semi-auto cut and tends to smooth out cycling across a wide range of loads. This is the exact same bolt carrier group Spike's uses in the rifles rolling off their own line, so you know it earned its spot.
The carrier is machined from 8620 tool steel and the bolt itself is cut from Carpenter No. 158 steel, shot peened, then individually High Pressure Tested and Magnetic Particle Inspected. That HPT/MPI process is the real deal for catching hidden flaws before a bolt ever makes it to your rifle, and it's a big part of why this BCG has a reputation for going the distance. The gas key is tool steel, chrome lined on the interior to fight carbon buildup, attached with Grade 8 hardware and properly staked so it stays put round after round.
The whole assembly wears a heavy MIL-STD-171 phosphate finish inside and out, with a hard chrome bore on the carrier to keep cleaning quick and cycling consistent. Worth knowing up front, this phosphate coating runs on the heavier side, so a microfiber cloth beats paper towels when you're wiping it down. The extractor is tool steel with a black spring insert and a Viton o-ring for extra tension, which keeps extraction reliable no matter what you feed it.
A nice touch is the laser-engraved ST spider logo on the right side of the carrier, positioned so it peeks through the ejection port door when the action is closed. Assembled it weighs in right around 11.6 ounces, and it drops straight into any mil-spec AR-15, M16 or M4 upper. Whether you're finishing a fresh build or swapping out a sketchy commercial carrier, this one is a solid, no-drama upgrade.
Yes, it drops straight into any mil-spec AR-15, M16 or M4 upper receiver with no fitting required. It comes fully assembled and tested, so you just slide it in and go. Since it uses the M16 full-auto carrier cut, it runs in both semi-auto and full-auto uppers.
The ST5BG01 is built for .223 Remington and 5.56x45mm NATO, and it will also run .300 AAC Blackout since that round uses the same bolt face. That covers most standard AR-15 builds on the 5.56 platform. It is not made for larger cartridges like .308 or 6.5 Creedmoor.
HPT stands for High Pressure Tested, where each bolt is proof fired with an overpressure round, and MPI stands for Magnetic Particle Inspected, which uses magnetic fields to reveal cracks invisible to the eye. Every bolt in this Spikes Tactical BCG goes through both individually. It is one of the best ways to catch a flawed bolt before it ever ends up in your rifle.
The MIL-STD-171 phosphate on this carrier group is a heavy coating, which is great for durability but a little rougher in texture than a slick nitride or nickel boron finish. Some folks find it grabs at paper towels, so a microfiber cloth or a good solvent works better for wipe-downs. The chrome-lined gas key interior helps keep carbon buildup manageable.
| UPC | 855319005495 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | ST5BG01 |
| Caliber/Gauge | .22 Caliber |
| Color | Black |
| Model | |
| Product Type | Bolt Carrier Group |
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