The FMK AR1 eXtreme is a multi-caliber, Mil-Spec, AR15 Lower Receiver, manufactured in the USA of a high impact proprietary composite polymer. The key to a good AR build is the lower receiver and the AR1 eXtreme is the strongest composite polymer lower on the market. Made in America, it comes with a lifetime warranty.

The FMK AR1 eXtreme Polymer AR Lower: Strong and Light

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. If you are looking for a light weight build, this is a great place to start.

I believe that a high strength polymer AR lower will build a great gun. The precision is evident through the entire lower and the built in trigger guard makes the build that much easier. I will be putting this lower into a build which will be light but I am not going for an extreme light weight build.

The FMK AR1 eXtreme Polymer AR Lower: Strong and Light


  • 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.”
The FMK AR1 eXtreme Polymer AR Lower: Strong and Light

The AR1 eXtreme has a metal plate embedded under the selector on the right side of the receiver with the serial number.

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

MSRP: $59.95

Download “AR1 eXtreme” AR1eX-2.pdf  the

You can learn more about AR1 HERE

If you are building a light build, there is a handy on-line AR weight calculator HERE