The Primary Weapons Systems MK109 Mod 1-M Upper Receiver (brand part no. MK1-M1U-300BLK-9) is a complete upper chambered in .300 AAC Blackout, built around a 9.75-inch, 1:8-twist barrel.

Key Specifications

• Chambered in .300 AAC Blackout.
• 9.75-inch barrel length.
• 1:8 twist rate.
• Ships as a complete upper receiver.
• Model: MK109 Mod 1-M.
• Sold under Primary Weapons Systems.
• At 9.75 inches, this barrel is well under the 16-inch federal minimum rifle-barrel length.

Frequently Asked Questions

Does this include a lower receiver? No, this is sold as a complete upper only; a compatible lower is required to complete a firearm.

Can I build this into a rifle-configured firearm? This upper’s barrel measures 9.75 inches, well under the 16-inch federal minimum for rifles. Pairing it with a shouldered rifle-configured lower without an approved NFA registration would create a Short-Barreled Rifle; it is legal to build as a pistol on an unregistered lower or as a registered SBR.

What caliber and twist does this use? It is chambered in .300 AAC Blackout with a 1:8 twist rate.

Buy the PWS MK109 Mod 1-M 300BLK Upper, 9.75in

Build a compact .300 Blackout upper around PWS’s complete MK109 Mod 1-M 9.75-inch assembly. Browse more of our AR15 uppers selection. Order the PWS MK109 Mod 1-M 300BLK Upper, 9.75in today for fast, insured shipping from a Lubbock, TX gun shop.