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KNS Precision built this adapter for guns that use an AR-style buffer tube socket to mount a stock but don't actually need that tube to house a buffer spring or recoil system. Think SIG MCX platforms, the Rattler, and other guns with a similar rear architecture. Instead of running a full-length buffer tube, this compact piece bolts straight into the threaded socket and gives you a 1913 Picatinny rail in its place, opening the door to folding stocks and braces like the SIG MPX or SB Tactical FS1913.
The design is refreshingly simple, which is a big part of why it works so well. An externally threaded plug screws into the buffer socket or ring, and a separate rail section slides into a slot on that plug. A hex-socket bolt and lock washer clamp the two pieces together and lock the whole assembly to the receiver. It's machined from aluminum with a matte black finish, so it adds almost no weight while standing up to regular range use and rough handling.
What sets the flanged version apart from the plain adapter is a small but important feature built into the base of the rail plate. That flange retains the standard AR15 takedown pin, detent, and spring, essentially doing the job of a rear takedown plate on lowers that rely on that hardware. It's a small design tweak, but it's the difference between an adapter that just adds a rail and one that keeps your lower functioning the way it's supposed to.
This is not a drop-in part for a standard direct-impingement AR15 upper and lower combo, since those rifles need the buffer tube to house the buffer spring and system. It's meant specifically for firearms where the bolt carrier and buffer assembly don't need to travel into or past the receiver ring. The kit ships as the adapter plug, rail section, hex bolt, and lock washer only, so your lower receiver, stock, and brace are separate purchases.
No, this adapter is not meant for a standard AR15 lower paired with an MCX upper. It's built for firearms where the bolt carrier and buffer tube don't need to travel past the receiver ring, so a typical direct-impingement AR15 setup won't cycle correctly with it installed.
The compact version keeps the same two-piece design and flange, but trims down the rail length so it doesn't extend back and lock into the rear AR15 receiver stock plate pocket. It's a good pick if you want the same functionality in a shorter, lower-profile package.
Anything with a standard Picatinny or 1913 mounting interface will work, including popular options like the SIG MPX folding stock or the SB Tactical FS1913 brace. Just double check the specific stock or brace you're eyeing uses that same rail attachment style.
The flange doesn't replace the takedown pin itself, but it does retain the detent and spring on lowers that rely on that hardware, similar to how a rear takedown plate functions. That keeps your lower running normally instead of losing that piece to the buffer tube swap.
| UPC | 853906008829 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | Compact AR-MCX Adapter with Flange |
| Color | Black |
| Model | |
| Product Type | Adaptor |
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