Fmk Ar15 Polymer Lower Receiver Bb
FMK Firearms
$37.69
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FMK Firearms
Fmk Ar15 Polymer Lower Receiver Bb
The FMK AR-15 Polymer Lower Receiver delivers a rock-solid foundation for your custom AR-15 build, combining cutting-edge composite polymer engineering with full MIL-SPEC compatibility and a lifetime warranty backed by American craftsmanship.
- Proprietary high-impact composite polymer withstands extreme conditions without cracking
- Incredibly lightweight at just 4.3 oz — less fatigue on long range days
- Accepts all standard MIL-SPEC uppers, including calibers up to .50 Beowulf
- Compatible with most AR-15 lower parts kits, grips, and stocks
- Resilient flex-back design — bounces back to shape instead of denting or breaking
- Proudly manufactured in the USA with an unconditional lifetime warranty
Who This Is For
The FMK AR-15 Polymer Lower Receiver is ideal for budget-conscious builders, competition shooters, and tactical enthusiasts who want a lightweight, durable lower without sacrificing MIL-SPEC compatibility. Whether you're putting together your first AR-15 build or adding a dedicated lightweight upper for 3-gun competition, the AR1 eXtreme gives you a dependable, American-made foundation that can take a beating in the field.
Specifications
| Brand | FMK Firearms |
|---|---|
| Model | AR1 eXtreme |
| Material | Proprietary High-Impact Composite Polymer |
| Weight | 4.3 oz |
| Compatibility | MIL-SPEC AR-15 Uppers up to .50 Beowulf |
| Parts Kit Compatibility | Most Standard AR-15 Lower Parts Kits |
| Country of Manufacture | USA |
| Warranty | Unconditional Lifetime Warranty |
| Finish | Matte Black |
| Category | Stripped Lower Receiver |
Frequently Asked Questions
Is this lower receiver compatible with my existing AR-15 upper and parts kit?
Yes. The FMK AR1 eXtreme is designed to accept all standard MIL-SPEC AR-15 upper receivers, including those chambered in calibers up to .50 Beowulf. It is also compatible with most commercially available AR-15 lower parts kits, aftermarket grips, and collapsible or fixed stocks. Always verify specific component fitment with your parts kit manufacturer for best results.
How does a polymer lower compare to an aluminum lower in terms of durability?
FMK's proprietary composite polymer is engineered to flex and return to its original shape under impact, rather than denting or cracking like traditional aluminum lowers can. While aluminum remains the standard for many builds, FMK's AR1 eXtreme is specifically formulated to match or exceed the durability of standard aluminum lowers while offering significant weight savings — making it an excellent choice for lightweight builds.
Does this lower come with a lower parts kit installed, or is it a stripped receiver?
The FMK AR-15 Polymer Lower Receiver is sold as a stripped lower receiver, meaning it does not include a lower parts kit (LPK), stock, grip, or buffer assembly. You will need to source these components separately to complete your build. This gives you the flexibility to customize your AR-15 with your preferred trigger group, grip, and stock configuration.
