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The Sierra K is B5 Systems' answer to a common headache: how do you get a real, shoulderable stock onto a truly compact AR without ending up with something clunky? This one is built specifically for PDW and short-barrel weapon systems, with a reduced overall footprint that keeps your rifle or pistol trim without giving up a solid cheek weld. At 5.63 inches long and just 6.6 ounces, it stays out of the way until you need it.
The body runs a slim, ergonomic cheek profile that gives you a repeatable weld even when the platform is short and busy. The low-profile adjustment latch sits flush and snag-free, so it won't grab plate carrier straps, slings, or clothing when you're moving fast or working in tight spaces. An anti-slip buttpad keeps the stock planted on your shoulder, which matters more than people expect on lightweight, punchy short-barrel builds.
B5 built in ambidextrous fixed sling loops along with limited-rotation QD sockets, so you can run whatever carry setup fits your role without adding hardware. Internal tensioners lock the stock tight to the receiver extension and cut down on the rattle and wobble that plague a lot of collapsible options. It's made in the USA from mil-spec materials with color-matched steel hardware, and it carries B5's limited lifetime warranty.
Here's the part worth knowing before you order: the Sierra K reaches its shortest collapsed length when paired with the Sierra K Receiver Extension Kit, which is a proprietary reduced-length setup sold separately. It will slide onto a standard mil-spec buffer tube for compatibility, but it won't fully collapse that way. If a genuinely compact package is your goal, plan on the matching extension kit to get the most out of this stock.
No, this listing is for the Sierra K stock only. To get the shortest possible collapsed length, you'll need the Sierra K Receiver Extension Kit, which B5 Systems sells separately. That kit includes the reduced-length receiver extension, a short heavy buffer, spring, castle nut, and end plate.
Yes, the Sierra K will mount to a standard-length mil-spec buffer tube and function fine. The catch is that it won't fully collapse on a standard tube, so you lose the compact benefit that makes this stock worth running. For a truly short setup, pair it with the matching Sierra K extension kit.
It comes with ambidextrous fixed sling loops built into the body plus limited-rotation QD sockets. That means you can set up left or right-handed carry and choose between a fixed loop or a QD swivel without buying extra hardware. It's a flexible setup for one-point, two-point, or bungee slings.
The Sierra K weighs 6.6 ounces and measures 5.63 inches long, 1.5 inches wide, and 3.8 inches tall. That keeps it light and trim on a PDW or short-barrel build. Despite the compact size, the slim cheek profile still gives you a comfortable, repeatable cheek weld.
| UPC | 814927024748 |
|---|---|
| Manufacturer | |
| Manufacturer Part Number | SRK1655 |
| Color | Black |
| Model | |
| Product Type | Stock |
| Length | 5.63" |
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