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B5 Systems built the Sierra K for folks who want their AR as short and handy as possible without ending up with a stock that feels like an afterthought. It's a compact, low-profile buttstock aimed squarely at PDW and compact weapon builds, and it manages to keep a usable cheek weld and a real shoulder surface even with the trimmed-down footprint. Weighing in at 6.6 ounces with a 5.63 inch length, it's the kind of piece that disappears into a build meant to be run tight and suppressed.
The slim cheek profile is the standout here. A lot of compact stocks force you to choose between short and comfortable, and this one splits the difference well. The low-profile adjustment lever sits flush enough that it won't hang up on gear, slings, or a plate carrier when you're getting in and out of position. Internal tensioners keep the fit tight to the tube so there's no rattle or wobble, and the anti-slip buttpad gives you something grippy to plant in your shoulder pocket during quick strings.
Sling attachment is genuinely versatile. You get integral fixed sling mounts on both sides along with limited-rotation QD sockets, so lefties and righties both have solid options and you're not stuck buying extra hardware to run the sling method you prefer. The hardware is color-matched steel, the materials and finishes are mil-spec, and the whole thing is made in the USA and backed by B5's reputation for parts that hold up to real use.
Here's the important part on fit: the Sierra K rides on a mil-spec diameter tube and mounts via the shortened Sierra K Receiver Extension Kit, which is sold separately. That kit is what gets you the truly compact collapsed length this stock was designed around. You can run it on a standard-length mil-spec buffer tube, but it won't fully collapse that way, so plan your build accordingly if minimal length is the goal.
No, this listing is for the stock only. The Sierra K mounts on a mil-spec diameter tube and is designed to pair with the B5 Systems Sierra K Receiver Extension Kit, which is sold separately. That kit includes the shortened receiver extension, buffer, spring, castle nut, and QD end plate.
You can, and it'll function fine as a slim, lightweight stock. The catch is that it won't fully collapse on a standard-length tube. If you want the shortest possible collapsed length, you'll want the Sierra K Receiver Extension Kit that the stock was built around.
It's purpose-built for PDW and compact weapon systems, which makes it a natural fit for short-barreled and suppressor-hosting AR builds. The reduced size and slim cheek profile keep things maneuverable in tight quarters. It's less about a general-purpose carbine and more about builds where minimal bulk matters.
Yes. It has integral fixed sling mounts on both sides plus limited-rotation QD sockets, so the sling setup is fully ambidextrous. Whichever hand you run and whichever sling method you prefer, you're covered without adding extra hardware.
| UPC | 814927024762 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | SRK-1657 |
| Color | Coyote |
| Model | |
| Product Type | Stock |
| Length | 5.63" |
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