PWS MK109 MOD 1-M Complete Upper Receiver - .300blk 9.75" Barrel

$1,099.95

This PWS MK109 MOD 1-M is a Mil-Spec long-stroke piston upper receiver. Basically, if an AK and an AR had a kid together, it would be a PWS rifle. The barrel is 9.75″ and is chambered in .300 AAC Blackout.

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This product can expose you to chemicals which are known to the State of California to cause cancer and birth defects or other reproductive harm. For more information, go to www.P65Warnings.ca.gov.

PWS MK109 MOD 1-M Complete Upper Receiver - .300blk 9.75" Barrel

How the PWS long stroke piston system works

Photo Credit: Primary Weapons Systems

The PWS MK1 MOD 1-M line features the PWS long stroke piston system. Internally, this line offers the tried and true system that PWS owners have grown to know and love. Featuring a free-float MLOK handguard, forward assist controls, and a more true to-mil-spec design, the MK1 MOD 1-M line is a go-to for not only civilians but also Law Enforcement. With the fully forged upper and lower receivers, the MK1 MOD 1-M is a no-nonsense tool for when you need a high-value option that is relentless and unstoppable. PWS produced an excellent video featuring a 3D cutaway rifle and how the long-stroke piston system works. The pictures below are screenshots from that video.

Primary Weapons Systems approached the AR15 from the perspective of AK47 owners. Why can’t an AR have the same kind of long-stroke piston system as an AK? Spoiler alert: it can, and it’s fantastic.

PWS Long stroke Piston system cutaway example 1
How the PWS long stroke piston system works

Photo Credit: Primary Weapons Systems

 Featuring a 3-setting adjustable gas system for users with suppressors, free-float M-LOK handguard, Radian Raptor charging handle, T6 7075 Forged upper receiver that integrates an extremely solid handguard attachment system. The PWS MK 1 -M line is designed to Mil-Spec standards, with higher-end parts and quality controls compared to the PWS Pro line. As with all PWS complete upper receivers, they will fit seamlessly on any AR15 lower receiver with no need for added accessories or modifications. 

PWS Long stroke Piston system cutaway progressive venting
How the PWS long stroke piston system works

Photo Credit: Primary Weapons Systems

MK109 MOD 1-M Upper .300 BLK Specs:

  • SKU: 18-M109UB0B UPC: 811154030399
  • Operating System: PWS Long Stroke Piston System, 3 setting Adjustable Gas Regulator
  • Caliber: .300BLK
  • Barrel Length: 9.75”
  • Gas System Length: Pistol
  • Barrel Twist Rate: 1:8
  • Muzzle Velocity: 2216 fps
  • Muzzle Device: PWS Triad 30 
  • Upper Receiver: PWS Proprietary Piston Upper, T6 7075 Forged, Anodized
  • Handguard: PWS M-Lok™ 6.9” Handguard (1.7” width, 2.25” height)
  • Charging Handle: Radian Raptor™ Ambidextrous Charging Handle
How the PWS long stroke piston system works

Photo Credit: Primary Weapons Systems

PWS MK109 MOD 1-M .300 BLK Upper Receiver Specifications

UPC: 811154030399 Manufacturer: Primary Weapons Systems
Manufacturer Part Number: 18-M109UB0B Type: Complete Upper Receiver
Barrel Length: 9.75" Receiver Material: T6 7075 Forged Aluminum
Gas System: PWS Long Stroke Piston System Caliber: .300 AAC Blackout
Color: Black Finish: Type III hardcoat anodized
Rail: PWS M-Lok™ 6.9” Handguard (1.7” width, 2.25” height) Barrel Twist Rate: 1:8
Charging Handle: Radian Raptor™ Ambidextrous Muzzle Device: PWS Triad 30

Frequently Asked Questions

*WE ARE NOT LAWYERS AND THIS IS NOT LEGAL ADVICE*

Technically, no you don’t need a permit. However, if you put this upper on a non-registered lower receiver with a stock on it, congratulations, you just made a short-barreled rifle, according to the ATF, and you can go to prison for it.

However again, if you put this upper on a registered “pistol” lower with (or without depending on the mood of the ATF that day) a pistol brace, you’re fine. Here is a very helpful video from Firearms Unknown explaining the facts.

.300 BLK or officially .300 AAC BLACKOUT, is basically a .30 caliber bullet smashed into a 5.56 case. It was designed to be a subsonic (slower than the speed of sound) bullet for close to medium-range engagements. This is basically a THICC bullet that’s supposed to be super hard-hitting and super quiet. Rumor has it that some dudes that officially don’t exist have come to really love .300 BLK for their sleepover parties.

Here’s a video from Vortex Nation talking about it.

Direct impingement means that the gases generated from firing a bullet are redirected through a gas tube. The gas tube feeds back into the upper receiver at the top of the bolt carrier group. When the gas pushes against the bolt carrier group, it causes it to eject the spent casing in the chamber and then feed the next round from the magazine. 

A long-stroke piston system is basically a normal BCG with a long steel rod attached where the gas key would typically be. The piston goes into the same area of the receiver as a standard gas tube, but it’s about twice as large. When you fire a round, the pressure of the gasses pushes against the piston and then vents out through ports in the gas tube. This allows the rifle to run extremely cleanly and efficiently rather than basically vomiting all over itself after every shot like a DI gun.

Another term for this is “piston gun.” 

If you genuinely didn’t know that, I would highly recommend checking out this “How an AR-15 Works” video animation. It’s AWESOME. Also, check out “Inside Primary Weapons Systems…” for PWS specific knowledge.

Also, if you’re brand new to the AR-15 world, I recommend checking out Palmetto State Armory. You can get a complete rifle for less than the price of this upper receiver. That’s not to say this is a ripoff, it’s just more of a high-end upper, whereas PSA is more entry-level. 

Yes! This is an upper receiver only and there are no regulated parts that would need to go through an FFL. You’re good to go!

We typically get products packed and shipped on the same day if you order before 3 EST. If not the same day, it will go out the next business day. We use FedEx for most of our hard goods, and a signature will be required for this.

We require adult signatures for orders over $500. This upper isn’t cheap, and I’m sure you don’t plan on donating it to your local porch pirate.

Yes! This is a 16.1″ barrel upper receiver, which is legal in all 50 states. (we are NOT lawyers, so do your own research if you aren’t sure.) The ATF may change their mind tomorrow and not bother telling anyone about it, but for now, you’re good to go. 

No, we strictly ship within the United States only.

Yep! We also don’t charge any kind of restocking fees or other nonsense. If you have an issue, we will do our best to get you squared away. Don’t take advantage of us, and we won’t take advantage of you. :)

No, this is an AR15 upper receiver only. There are no regulated parts that would require an FFL transfer. This can ship straight to your front door.

No, this is an AR15 upper receiver only. No sights or any other greyed-out parts are included. 

Yes, this 19-PM116UA0B upper receiver ships with a PWS Long Stroke piston system, full auto-capable bolt carrier group and Radian Raptor™ ambidextrous charging handle. Drop it on any lower receiver, throw an optic on, and you’re good to go. 

ABSOLUTELY NOT. This is an upper receiver only. Both the BCG and barrel are designed to be fully functional with full auto and burst fire lower receivers, but the upper does NOT have any full auto capabilities out of the box.

As long as your lower is within normal AR15 specifications, this PWS MK116 upper receiver should work just fine. Honestly, if it doesn’t work with your lower, you might want to get a new lower…

Magnetic particle inspection is a non-destructive test (NDT) that is done to find microscopic cracks and imperfections in the metal. The process involves electro magnates and tiny magnetic particles suspended in an ultra violate light-sensitive liquid. It can also be done with magnetic powder with similar results. 

The image below shows what cracks look like during the test. It is a screenshot from this video by MaterialsScience2000.

The forward assist is the small button sticking out the back right side of the upper receiver. It is designed to help push the bolt carrier group into battery (locked into place properly) if the receiver is full of dirt or other junk. Basically, it helps keep the rifle in the fight if you’re in some seriously bad conditions. 

If you genuinely didn’t know that, I would highly recommend checking out this “How an AR-15 Works” video animation. It’s AWESOME.

PWS rifles are made in the United States. Specifically, they are made in Boise Idaho.

M4 feed ramps are basically extended ramps from the barrel extension that cut into the lower receiver. When Colt came out with the M4 carbine, the shorter barrel and gas system was causing some feeding issues where the bolt was moving faster than the magazines could keep up. 

The M4 ramps basically create a longer, smoother ramp for the cartridges to slide into the chamber. 

Hardcoat anodizing is a process of using sulfuric acid and electricity to create a hard oxide film over the part. Here is an in-depth article on hardcoat anodizing if you want to dig deeper. 

M-Lok™ refers to the type of attachment system used for accessories on the rail. Magpul invented and patented the Modular Lock (M-Lok) system.

Free float is referring to the way the rail attaches and interacts with the upper receiver and barrel. When you fire a bullet through a barrel, the barrel vibrates and moves in very specific ways. If the handguard or rail is physically touching the barrel, any interaction you have with that handguard will negatively affect the rifle’s accuracy. With a free float rail, the barrel is completely free to vibrate and move consistently, which drastically improves repeatable accuracy. 

Weight 4.25 oz
Dimensions 0.00 × 0.00 × 0.00 in
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Size Chart

Chambered in .300 AAC Blackout. This PWS MK109 upper will work on any standard AR15 lower receiver. Make sure you understand your local, state, and federal laws regarding short-barreled rifles and pistols before purchasing.

PWS MK109 MOD 1-M Complete Upper Receiver - .300blk 9.75" Barrel

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