FMK AR1 eXtreme Lower Receiver

November 14, 2018





   FMK Firearms, is a US Based Company located in California, that specializes in Manufacturing Their own Firearms. They Started First in the Pistol Making business and are now Moving into the Ar15 side of the Market.





   FMK Has Released an Ar15 Lower Receiver. I know exactly what you are thinking, "Great, Just what we need, Another mil spec ar15 Lower Receiver"! Well, you're half right.

   There Ar15 Lower Receiver is Mil Spec, but it is anything but ordinary.




The FMK AR1 eXtreme Lower Receiver comes in two Colors,





The AR1 eXtreme Lower Receiver is made from high impact, proprietary composite polymer material. While weighing significantly Less than a mil spec lower receiver, the ar1 extreme weighing in at a  mere 4.3oz.

   FMK claims that their state of the art polymer allows for superior strength and unmatched durability. they believe the ar1 extreme to be the strongest composite polymer lower on the market today.





   while working with the ar1 extreme lower receiver and putting it all together. I ran into very little problems at all compared to aluminum lower receivers.

   if you build these rifles for a living or a hobby, you have definitely ran into problems before with aluminum lower Receivers. building the ar1 extreme, i had to run a drill bit down some of the detent holes to clear out some shavings that were stuck, because the detent would not go in. but that is nothing to complain about. all the holes in the Ar1 eXtreme lower Receiver were in the correct spots and the correct depths.







   Since this ar1 extreme lower receiver only weighs 4.3oz, i decided this would be the perfect lower for my lightweight build. since the Ar1 extreme lower receiver is made from a high impact polymer, it makes perfect sense to use this lower receiver in a build that will run into high impacts every now and then. lol i thought it best to go with a polymer upper receiver to match the lower and save significant weight.

   After i completed my lightweight build, i placed a full 30rd 5.56mm magazine into the lower to feel the weight of it. as i held the rifle in shooting stance, i could not believe how lite the rifle was. i even had to check the magazine a few times to make sure it was still full!

   the rifle weighs so little you barely notice your still holding 



Final Weigh in 

Complete Rifle with F/R Sights

and Front Barricade Grip

5 lbs 12 1/2 oz



Complete Rifle with F/R Sights, Front Barricade Grip and

Eotech Red Dot Sight 

6 lbs 5 oz



Complete Rifle with F/R Sights, Front Barricade Grip, Eotech Red Dot Sight and Full Gi 30rds xm855 5.56mm Magazine 

7lbs 10oz







   So, After Thoughts???


  • I really like how FMK made the ar1 eXtreme Lower Receiver to mil spec. Most receivers that say mil spec are not. The biggest is how the trigger group area is Cut. Most Lowers are cut too AR15 specs. The AR1 eXtreme is cut to M4 Specs. So if you even want to register this lower as a full auto Lower, Everything will drop right in except for the sear pin hole that must be drilled. 

  • I love the weight of the AR1 eXtreme Lower Receiver, its So Lite but still very durable.

  • I Shot Multiple types of Ammo using this Build, Armscor 55gr,  Xm855 62gr and even Armscors Vmax 5.56mm Ammo and I did not have any problems with this lower.

  • The Lower held its own, even when torquing the Castle Nut on the Buffer Tube I over torqued it just to see if something would break but nothing did.

  • I would of liked to see Metal or Brass inserts at Failure Points like the Buffer Tube Threads and Front Take Down Pin Lug in the AR1 eXtreme Lower Receiver .







FMK Firearms warrants to you, the original purchaser of a new firearm, that for ten years from the date of purchase in the United States, your FMK firearm will be free from defects in material and workmanship.








AR1 eXtreme


Multi-Caliber, Mil-Spec, AR15 Lower Receiver, manufactured in the USA of a high impact proprietary composite polymer. This state of the art polymer allows for superior strength, unmatched durability and is extremely lightweight only 4.3oz. The AR1 eXtreme is by far the strongest composite polymer lower on the market today. The key to any good project is the foundation and on an AR15, that is the lower receiver. The Ar1 eXtreme comes with a lifetime warranty; and of course, it’s Proudly American.







  • Superior strength – Built with proprietary composite polymer to withstand extreme conditions.

  • Unmatched durability – When most lowers dent or break the AR1 eXtreme bounces back to shape.

  • Extremely lightweight – 4.3oz • Accepts all standard MIL SPEC uppers up to .50 Beowulf

  • Compatible with most current AR15 lower parts kits, grips and stocks.

  • Unconditional lifetime warranty.

  • Custom engraving – “The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants.”




  • Frame: High Impact Proprietary Composite Polymer

  • Caliber: Multi-Caliber

  • Size: MIL SPEC

  • Weight: 4.3oz

  • Colors: Black and Dark Earth

  • 100% USA Made

MSRP: $59.95




AR1 eXtreme pdf




FMK Firearms, Inc. 

Consumer Service Department

1025 A Ortega Way

Placentia, CA 92870







Armscor  supplied the Ammo used throughout this T&E Review.

Thank You



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