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Primary Weapons Systems MK111 Piston Upper (11.85" 300 Blackout Barrel)

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Primary Weapons Systems MK111 Piston Upper (11.85" 300 Blackout Barrel)

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$1,349.95 $999.95

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MPN: M111UB0B / 2M111UB0B


  • PWS long-stroke piston system - combines the agility of the AR-15 with the reliability of the AK-47 into a sleek and efficient design
  • Continuous Picatinny top rail
  • Free Float KeyMod system w/ PicMod Technology in MOD 2 models - The new technology allows you to mount KeyMod attachments anywhere on your handguard and mount Picatinny accessories directly to the recessed Picatinny rail section at the end of the handguard
  • Lightweight forged upper in MOD 2 models - No forward assist and material removed from less structurally important location for weight reduction
  • Increased carrier mass to extend dwell time and delay unlock
  • Lithium Embedded Salt Nitro-Carburized (FNC LIFE HD) coated barrel and bolt carrier for durability, corrosion resistance and to reduce friction


  • Caliber: 300 Blackout
  • Finish: Type III Class 2 Hardcoat Anodized Finish
  • Upper Receiver:
    • MK1 MOD 1-P: Forged Flat Top Upper - Made from 7075-T6 aluminum
    • MK1 MOD 2: Forged Lightweight Flat Top Upper (No forward assist) - Made from 7075-T6 aluminum 
  • Handguard:
    • MK1 MOD 1-P: 10-inch KeyMod Rail System - Made from 6061-T6 aluminum
    • MK1 MOD 2: 11-inch KeyMod Rail System with PicMod Technology - Made from 6061-T6 aluminum
  • M4 Feed Ramps: Yes
  • Muzzle Device: PWS Triad 30 flash suppressor
  • Barrel: 11.85” 1:8 Twist Modify Low-Stress profile 300 Blackout 416R Stainless Steel Barrel (Black finish)
  • Muzzle Thread Pattern: 5/8"-24
  • Gas Block: PWS Long Stroke Piston System (Non-adjustable gas block. Adjustment know is for disassembly and cleaning only)
  • Gas Length: Pistol-Length
  • Bolt Carrier Group: PWS Long Stroke Piston Bolt Carrier Group
  • Charging Handle: Bravo Company Mod4 Extended Charging Handle
  • Weight: 
    • MK1 MOD 1-P: 3 lbs. 12.7 oz.
    • MK1 MOD 2: 3 lbs. 9.9 oz.
  • Overall Length: 20.6"


  • 3x RailSacles covers
  • 1X PWS gas adjustment tool

*This upper receiver assembly has a barrel that is shorter than 16". This upper is only for use on AR pistol lower receivers and NFA registered Short-Barreled Rifle (SBR) lower receivers. All NFA laws apply!




In the PWS MK111 300 Blackout Upper, Primary Weapons Systems offers a high-quality long stroke piston system with an 11.85-inch 416R stainless steel barrel chambered in 300BLK. This is a compact 300 Blackout upper that still functions well under suppression and has been field proven by a number of operators in real-world situations, even at distances as far as 300 meters. The MK111 is a variation of the Primary Weapons System MK1 long piston upper system.

In designing the MK1 Upper, Primary Weapons System sought to bring the nearly infallible reliability of the AK-47 and the agility and adaptability of the AR platform together to create an advanced upper that is more reliable than direct impingement gas operated uppers and more ergonomically forgiving than the stolid AK. The result is an upper that operates well with less total pressure than direct impingement systems, has fewer moving parts and requires personal maintenance to keep it in excellent working order. The MK1 has a better service life and fewer issues with fouling than its predecessors, freeing the operator actually complete his mission rather than pampering a finicky firearm.

In the PWS MK1, Mod 1 certain vestiges of the previous generation held on. If you prefer a blockier upper and you’re hooked on the promise of the forward assist, the Mod 1 is for you. If you’re ready to let go and step further into the future where the competition doesn’t dare go, take hold of the next evolutionary rung and try a PWS MK1 Mod 2. The PWS MK1 Mod 2 300 Blackout upper features a surface machined forged receiver without a forward assist. The resulting loss of mass easily approaches the standard set by machined billet receivers but does so with the superior strength and service life of forged units. Both evolutions of the PWS MK111 Blackout use a gas block to help manage pressure, but unlike uppers chambered to .223, the block is not adjustable.

Because It’s Time… You know you want the reliability of the revolutionary PWS 300 Blackout piston upper, simply choose the model you’re most comfortable with and evolve.

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