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The Spike's Tactical STU5025M4S takes most of the guesswork out of building a solid 5.56 carbine. This is a complete upper assembly, meaning the barrel, bolt carrier group, charging handle, dust cover, forward assist, and handguard all come together and ready to go. Pin it to a standard AR-15 lower and you're set. It came out of Spike's ST-15 line that was originally built for law enforcement, so the whole thing is put together to Mil-Spec tolerances with no corners cut.
The heart of this upper is a 16" chrome-moly vanadium barrel with an M4 profile and a 1:7 twist rate. That twist handles the full range of common 5.56 loads, from lighter varmint-weight bullets up to heavier 62 and 77 grain projectiles, so you're not locked into one type of ammo. The bore and chamber are chrome lined for longer life and easier cleaning, the barrel is high pressure tested and magnetic particle inspected, and it wears a phosphate-finished A2 flash hider on 1/2×28 threads. A carbine-length gas system and pinned F-marked front sight base round out the barrel setup.
Spike's includes their Mil-Spec M16 profile bolt carrier group, built with a Carpenter 158 steel bolt that's HPT and MPI tested, with a properly staked gas key. That's the kind of BCG you want if reliability matters, and it means one less part to source separately. The receiver itself is machined from a 7075-T6 forging with a hard coat anodized finish, M4 feed ramps, and laser-engraved T-marks on the flat top rail for easy optic alignment.
Because everything ships assembled and function checked, this is a great pick for a first-time builder or anyone who wants a reliable carbine without chasing down individual parts. It drops onto any standard AR-15 lower and it's backed by the Spike's Tactical lifetime warranty.
Yes. This is a complete upper, so it ships with a Mil-Spec M16 bolt carrier group and a charging handle already included. The BCG uses a Carpenter 158 steel bolt that's high pressure tested and magnetic particle inspected. All you need to add is a lower receiver.
It's built to fit any standard Mil-Spec AR-15 lower receiver. The upper is machined from a 7075-T6 forging to Mil-Spec tolerances, so it mates up the same way a standard M4-style upper does. Just line up the takedown pins and you're good to go.
The 1:7 twist is the most versatile rate for 5.56, and it stabilizes everything from light 55 grain loads up through heavier 62 and 77 grain projectiles. Since it's chambered in 5.56 NATO, it will safely run both 5.56 and .223 Remington. Heavier match-grade bullets tend to shine with this twist.
The upper comes with a pinned F-marked A2 front sight base, so you already have a front sight out of the box. To complete your sight picture you'll want to add a rear sight or an optic to the flat top Picatinny rail. Laser-engraved T-marks on the rail make lining up an optic straightforward.
| UPC | 815648021030 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | STU5025M4S |
| Action | |
| Barrel Finish | Black Phosphate |
| Barrel Length | 16" |
| Caliber/Gauge | .223 REM/5.56 NATO |
| Color | Black |
| Product Type | Complete |
| Sights | A2 Front |
| Style | Complete |
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