Primary Weapons MK109 MOD 2-M .300 Blackout 9.75" AR-15 Piston Upper

The Primary Weapons Systems MK109 MOD 2-M is a purpose-built .300 Blackout complete upper receiver assembly engineered around PWS's signature long-stroke piston operating system. Designed to drop onto any standard AR-15 lower receiver, it gives the shooter a compact, dependable 300 BLK platform for home defense, hunting, and range use.

At the heart of the MK109 MOD 2-M is a 9.75" barrel chambered in .300 AAC Blackout, stabilized by a 1:8 twist rate that handles everything from lightweight supersonic projectiles to heavier subsonic loads. PWS's long-stroke piston drive routes propellant gas through a self-contained operating rod rather than bleeding it directly into the bolt carrier group, which significantly reduces fouling and heat soak and keeps the action running cleaner over extended sessions.

A 3-setting adjustable gas regulator lets the shooter tune the system for unsuppressed fire, suppressed fire with subsonic ammo, or a neutral middle setting, making this upper especially well suited to a short-barrel suppressed 300 BLK build. The upper receiver is surface-machined from forged aluminum and is built without a forward assist, trimming weight and cleaning up the right side of the receiver.

Out front, an 8.9" PWS PicLok handguard with full MLOK slots provides a slim, rigid mounting platform for lights, lasers, foregrips, and bipods. The muzzle is finished with the PWS Triad muzzle device, designed to reduce flash and help control recoil on a short-barrel package.

Upper receiver assembly only. AR-15 lower receiver and BCG sold separately.