The B5 Systems Sierra K is a compact rifle stock purpose-built for PDW platforms and short-barreled AR systems where space is at a premium. If you're running a SBR, pistol-caliber carbine, or other compact rifle setup and need a stock that won't add bulk or snag on gear, the Sierra K delivers a slim, purpose-driven profile designed around the realities of close-quarters and vehicle-based shooting. Its reduced footprint and streamlined cheek rest make it a natural fit for operators who prioritize maneuverability over traditional rifle ergonomics.

The Sierra K mounts via B5's shortened compact Mil-Spec receiver extension, so compatibility starts with confirming you have the right platform—this isn't a universal fit. Once mounted, you get a rock-solid platform with internal tensioners that eliminate rattle and keep the stock locked in place. The adjustment mechanism is stripped down to essentials: a low-profile latch that won't catch on plate carriers, sling mounts, and an anti-slip buttpad that stays put whether you're shooting from barricades or vehicles. Hardware is color-matched and finished to Mil-Spec standards, so you're not sacrificing durability for the compact form factor.

The Sierra K isn't designed to maximize cheek weld or comfort during long shooting sessions—it's engineered for the job it does: keeping your compact rifle light, snag-free, and ready to move. For PDW builds, short-range defensive carbines, or specialized tactical setups, this is a no-nonsense choice from a brand with deep roots in AR ergonomics and combat application.

Key Features

• Compact profile optimized for PDW and short-barreled rifle platforms
• Slim cheek design minimizes snags with gear and clothing
• Low-profile adjustment latch for streamlined operation
• QD and fixed sling mounts built in
• Internal tensioning system for rattle-free lockup
• Anti-slip buttpad for secure shoulder contact
• Mil-Spec materials and finishes throughout
• Color-matched steel hardware

Specifications

Frequently Asked Questions

What receiver extension do I need for the Sierra K stock?

The Sierra K requires a shortened compact Mil-Spec receiver extension. Standard rifle extension tubes will not work. You'll need to verify your upper is set up for a compact extension or obtain the B5 Sierra K Receiver Extension Kit.

Is the Sierra K right for a standard AR-15?

No. The Sierra K is purpose-built for compact platforms and PDWs that use shortened receiver extensions. It's not compatible with standard Mil-Spec rifle-length tubes used on full-size AR-15s.

What sling attachment options does it have?

The Sierra K includes both a QD (quick-detach) mount with limited rotation and integral fixed sling attachment points, giving you options for how you want to run your sling.

Does it reduce recoil impulse?

The Sierra K is designed for compact weapon systems where space is the priority. It does not include a buffer or recoil mitigation system—that function is handled by your receiver extension and buffer setup.