B5 Systems Sierra K Receiver Extension Kit

he Sierra K Receiver Extension Kit is the proprietary mounting system for the Sierra K Buttstock. It consists of a reduced-length, mil-spec diameter, 7075 aluminum, 5-position receiver extension, a short heavy buffer (3.5 oz), extra power spring, castle nut, and quick disconnect end plate.

The B5 Systems Sierra K stock provides a form factor that balances minimalist design with tactical sensibility. It is a purpose-driven compact stock, optimized for use on PDW and compact weapon systems. Features include reduced overall size and slim cheek profile, snag-free adjustment lever, limited rotation QD and integral fixed sling mounts, internal tensioners, and anti-slip buttpad.