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Geissele built the Super Modular Rail MK4 for folks who want a rail that disappears in the hands but never flinches under hard use. This 13.5-inch version wears a Desert Tan finish and runs Magpul's M-LOK attachment system at the 3, 6, and 9 o'clock positions plus the upper 45-degree quadrants, so you've got room for lights, grips, pressure switches, and a bipod without fighting for space. Up front, integrated short M1913 Picatinny sections at 3, 6, and 9 o'clock give you a spot to hard-mount gear that plays better on a rail than a slot.
The MK4 is machined from high-strength 7000-series aluminum and vented like crazy. That venting does double duty, shedding weight while letting barrel heat escape so your support hand and your accessories stay happier during long strings. The result is a slim, rigid tube that feels great whether you're shooting off a barricade or just carrying the rifle around all day.
The heart of this system is Geissele's proprietary 2.25-inch barrel nut. That extra length increases contact where the rail meets the receiver, which keeps the whole assembly straight and true down the full length of the free-float section. In plain terms, it locks in tight, holds your zero, and comes back to the same place if you pull the rail for maintenance. Anyone who has cursed a wobbly or shifting handguard will appreciate what this longer nut brings to the table.
The SMR MK4 shows up on serious AR-15 builds for a reason. It carries the same fit and finish reputation Geissele earned with their triggers, and it pairs naturally with clone-style and duty-focused rifles. If you want a handguard that stays out of the way, keeps things light, and gives you a stable platform for whatever optics and accessories you're running, this one earns its keep.
No. This SKU includes the handguard along with the proprietary barrel nut and mounting hardware, but the Geissele barrel nut wrench and a low-profile gas block are sold separately. Plan on picking up the correct Geissele wrench for install, and make sure your gas block fits under the rail.
It's built for standard AR-15 and M4-pattern uppers with mil-spec dimensions. Just double-check that your barrel's gas system length and your gas block profile work with a 13.5-inch free-float rail before install. The proprietary barrel nut replaces your factory nut during the swap.
You get M-LOK slots at the 3, 6, and 9 o'clock positions plus the upper 45-degree quadrants, so lights, hand stops, grips, and pressure switches all have a home. The integrated Picatinny sections at the muzzle end are handy for bipods and lights that mount better to a rail. There's plenty of room to tailor the setup to how you run the rifle.
The 2.25-inch barrel nut increases the surface contact between the rail and receiver, which keeps the free-float tube straight and rigid its full length. That translates to a rock-solid mount and repeatable zero, even if you remove the rail for cleaning or maintenance. It's a big part of why these rails have such a strong reputation for staying put.
| UPC | 854014005724 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | 05-278S |
| Color | Desert Tan |
| Length | 13.5 |
| Model | |
| Product Type | Handguard |
| Style | M-LOK |
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