First Responder/MIL/Veteran Discount


Locking: Holds QD in one of four positions

360° Rotating: Allows QD to spin freely in mount


2 Point Sling: Locking front 360 Rear

1 Point Sling: Locking Rear

Comp removal is the opposite of install.

  1. Place comp in vice using soft jaws or other protective material like our Muschi Mounting Block or leather.
  2. Tighten down comp sufficiently. There should be NO movement from the comp/barrel.
  3. Back the slide off and angle away from the barrel flats.
  4. Tighten adjustable wrench to barrel flats.
  5. Supporting the slide with your opposite hand, slowly turn the barrel loose. This will take some strength.
      1. If you aren’t confident/comfortable doing this, PLEASE contact us.
  6. Remove from vice, continue loosening comp by hand until removed.
There is no one answer to this question, factors such as barrel length, ammunition used, suppressor, air temp/pressure and how clean the rifle is will all be factors that play into the jet size that will work for your setup.  The best way to find out what size will work for you is by trial and error with a couple tests.
1. Load a full magazine for your rifle as well as one in the chamber for a total of 21 rounds(scar 17) or 31 rounds(scar 16).  Fire the rifle once paying attention to the ejection and make sure the next round in the magazine is stripped and loaded into the chamber.  If all looks good then move to #2
2. Now that the rifle has cycled another round, insert an empty magazine and conduct a lockback test by firing the rifle again.  If both these tests have passed you can move down a jet size and start over.  If your rifle has failed either of these tests, increase by a half jet size and conduct the tests again.

Scar 17 Factory jet size: 1.45mm (16″ Barrel)
Scar 20 Factory jet size: 1.4mm (20″ Barrel)
Scar 16 Factory jet size: 1.35mm (16″ Barrel)
Below PMM Address all the nuances of the MK17 & MK20  FN SCAR Gas System

Please check the appropriate product page, we have readily available PDF versions of our instructions and/ or tutorial videos.

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Orders over $35 will be shipped via USPS Priority Mail. Orders under $35 will be shipped via USPS First Class Mail. If you would prefer your items to be shipped via UPS Ground, contact
Once 20 calendar days have passed from the day of shipment, we are able to process these requests with our insurance. You will be required to complete an online affidavit in order to have your order replaced or refunded. Please contact to assist you in this matter.
If there is damage or loss to your order at the time of delivery, contact us as soon as possible. You will be required to provide photos as well as to complete an online affidavit in order to have your order replaced or refunded. Please contact to assist you in this matter.
Returns must be new and unopened/ unused, and purchased within the last 30 days. All components of the product are necessary in order to be eligible. All returns are subject to a 10% restocking fee– shipping costs are non-refundable. The customer must cover return shipping costs. It is imperative that you include a copy of your order invoice stating that it is a return. Please ship returns to:
Parker Mountain Machine
19 Fire Rd 13
Strafford, NH 03884
Our apologies. Please contact with your order number in order for us to correct our error quickly. You may be asked to provide photos so we can identify the product you were sent.
We are a small staff, and try to answer emails as quickly and thoroughly as possible. Office hours are Monday through Friday from 9am-5pm E.S.T. Emails received outside of office hours will be answered at our earliest convenience.
Please contact as soon as possible to assist you. Let us know you would like to change your order, and we’ll try to accommodate you.
If you just received your shipping confirmation email, we may be able to assist you if it is still in the building. Please contact as soon as possible to assist you. If your order has already been picked up by the carrier, we are unable to stop shipment. Once your order arrives, you will need to mail it to us for a return or exchange.
Parker Mountain Machine
19 Fire Rd 13
Strafford, NH 03884
Cancellation of an order will result in a 6% transaction fee. Shipping fees are fully refundable. For any cancellation queries, please contact
Exchanges must be new and unopened/ unused, and purchased within the last 30 days. Please contact with your order number to assure that we are able to accommodate your request. 

If your order has not shipped yet, please contact You will be asked to place an additional order. We will ship your items together and refund the difference in shipping costs. 


Federal American Eagle

Speer Lawman


Remington UMC

Sig Sauer





Speer Lawman

Federal American Eagle

Sig Sauer



Remington UMC


Ammo that is inconsistent:

115gr Winchester white box

115gr Blazer brass

Any re-manufactured ammo

PMM suggests only using a quality factory loaded ammo with our comps.

We clean our comps like we would a rifle with a muzzle device on it.  Run a bore snake through the barrel, let the port of the comp soak in some quality gun cleaner and scrub it out with a brush.  If the carbon is very built up you can let it soak then use a dental pick to remove the build up.
Once clean put a few drops of gun lube in the port and this will help make future cleanings easier.
If you remove the comp new shims will need to be installed since they act as a crush washer like system.