The FMK AR1 eXtreme is an AR15 Lower Receiver made from high impact proprietary composite polymer. I just put this lower together and I am impressed. The key to a good AR build is the lower receiver and the AR1 eXtreme is the strongest composite polymer lower on the market.

The big news is a weight savings of 4.4 ounces. The AR1 eXtreme weighs in at 4.3oz.  A milspec lower weighs 8.7 oz. My complete lower build came out to 1 pound and 10 ounces. There is more weight to be cut if I wanted to go extreme, but I am very happy with this result. If you are looking for a light weight build, this is a great place to start.

Building the FMK AR1 eXtreme: 1 lb 10 oz Complete AR Lower

I started with an Armaspec Gun Builder’s Lower Parts Kit  (less Fire Control Group & Grip) for .223/5.56 MSRP $54.50

Armaspec Stainless Steel Gun Builder’s Lower Parts Kit incorporates all the great products from Armaspec in one package.

If you want to chose your own grip, trigger and trigger guard, this is the way to go. This is not a complete lower parts kit. This is a builder’s kit. This Kit does not include the Pistol Grip, Pistol Grip Screw and Washer, Trigger and Hammer, Trigger and Hammer Springs, Disconnect, Disconnect Spring, Trigger Guard and Roll Pin. You won’t end up with extra parts, but you need to make sure you have all the parts.

Building the FMK AR1 eXtreme: 1 lb 10 oz Complete AR Lower

Available in Black, FDE, ODG, Red, Blue, Light Blue, Purple and Gold. I chose the gold to highlight the my FDE lower.

* Fits all milspec AR 5.56/.223
* Made in U.S.A
* Lifetime Warranty

1. Armaspec SFT 45/90 Safety Selector
2. Bolt Catch
3. Enhanced Take Down Pin
4. Stainless Steel Takedown detent
5. Takedown Detent Spring
6. Enhanced Pivot Pin
7. Stainless Steel Pivot Detent
8. Pivot Detent spring
9. Stainless Steel Anti-Walk Trigger Pin
10. Stainless Stainless Anti-Walk Hammer Pin
11. Stainless Steel Buffer Retainer
12. Magazine Catch
13. Magazine Spring
14. Enhanced Magazine Release Button
15. Stainless Steel Bolt Catch Detent
16. Stainless Steel Safety Selector Detent
17. Bolt Catch Roll Pin
18. Bolt Catch Spring
19. Buffer Retainer Spring
20. Selector detent spring
21. Hex Keys for Anti-Walk Pins

As a pistol grip, I selected the Mission First Tactical EPG16V2  AR15 grip. At a weight of 2.2oz it seemed like the perfect choice for this build. I like the 15 degree angle for feel and control and the texture provides a positive grip surface. There is a small tab which covers the receiver gaps that cause discomfort during sustained shooting. Because the FMK has a built in trigger guard, I cut off the tab for a perfect fit.

The obvious stock choice was the  ELF Ultralight Aluminum Stock, the lightest all metal adjustable stock in production, weighing just 5.2oz. This is a fixed stock so it does not run afoul of certain state bans. It is adjustable over the entire length of the buffer tube. It is silent, there is no clicking into detent holes, a simple turn of the knob allows full adjustment and when tightened, it is rock solid with no rattle.

The whole build came together with no issues, The FMK receiver is a true milspec and a quality parts kit like the Armaspec drops right in. I have never had a build go smoother. The polymer is self lubricating and makes the parts slide right in. I am starting with a standard trigger with the option to up grade later. I hate putting in the trigger guard roll pin, so it was a great relief that the AR1 eXtreme didn’t need those parts and the Armaspec builders kit didn’t have them.

I did a complete function check and everything looks great. The lower works great with a Mission First Tactical polymer magazine.

Specifications for the AR1 eXtreme:

  • Frame: High Impact Proprietary Composite Polymer
  • Caliber: Multi-Caliber
  • Size: MIL SPEC
  • Weight: 4.3oz
  • Colors: Black and Dark Earth
  • 100% American Made
  • Metal plate embedded in the receiver with the serial number

MSRP: $59.95

Made in America, it comes with a lifetime warranty.

If you are building your own light weight build, you can use the handy on-line AR weight calculator HERE

Range report coming soon!