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Geissele didn't cut corners with the Super Modular Rail MK4, and it shows the second you pick one up. This 13.5-inch M-LOK handguard is a genuine free-float design that keeps weight low while staying stiff enough to hold zero through hard use. You get M-LOK slots at the 3, 6, and 9 o'clock positions plus the upper 45 quadrants, so there's plenty of real estate for lights, lasers, hand stops, bipods, or whatever else you like to run out front. Up at the muzzle end, short integrated M1913 Picatinny sections at 3, 6, and 9 give you a spot for backup irons or gear that isn't M-LOK yet.
The heart of this rail is Geissele's proprietary 2.25-inch barrel nut. That longer nut spreads out the contact area where the rail meets the receiver, which is a big part of why the MK4 has a reputation for being straight, true, and genuinely rigid down its full length. Folks who've run other name-brand rails often notice the difference in stiffness right away. It also means your zero comes back reliably if you ever pull the rail for maintenance and reinstall it.
All those M-LOK slots and cutouts do double duty. They shave ounces and open the rail up for airflow, so the barrel sheds heat faster during longer strings of fire. The rail runs a slim profile with roughly a 2.11-inch outer diameter and a 1.35-inch inner diameter, giving it a comfortable, hand-filling but not chunky feel. Finished in Type 3 hardcoat anodize over aircraft-grade aluminum, it's built to take abuse and keep looking the part.
This one is designed around mil-spec M4-style upper receivers and works with standard low-profile gas blocks and gas tubes. It's a great pick for anyone building a lightweight carbine, a duty-style setup, or a precision-minded AR-15 where a repeatable zero matters. Keep in mind you'll want the Geissele barrel nut wrench on hand for install, since that tool is sold separately.
No, the barrel nut itself is included, but the Geissele barrel nut wrench is sold separately. You'll need that tool to properly torque the nut during installation, so plan on grabbing one if you don't already have it. It's a smart tool to own anyway if you're building or servicing Geissele rails.
It's designed to fit mil-spec M4-style upper receivers, which covers the vast majority of AR-15s out there. Compatibility with billet receiver sets can vary and may require minor fitting. It works with standard low-profile gas blocks and gas tubes, so most builds drop right in.
The extra-long barrel nut increases the contact surface between the rail and the receiver, which is what gives the MK4 its impressive rigidity. That translates into a handguard that stays straight and true along its full length. It also helps your zero return reliably if you ever remove and reinstall the rail.
Plenty. You get M-LOK slots at the 3, 6, and 9 o'clock positions plus the upper 45 quadrants, so lights, lasers, bipods, and hand stops all have a home. Short integrated Picatinny sections at the muzzle end handle backup irons or any gear that still runs on a 1913 rail.
| UPC | 854014005717 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 05-278B |
| Color | Black |
| Length | 13.5 |
| Model | |
| Product Type | Handguard |
| Style | M-LOK |
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