FF-ML 20 Inch 6.5 Grendel AR 15 Upper – 20 Inch Barrel by Faxon – 15 Inch M-LOK Free Float Handguard

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AT3™ AR-15 Bolt Carrier Group -  5.56 NATO/.300 Blackout - Black Nitride

AT3™ AR-15 Bolt Carrier Group - 5.56 NATO/.300 Blackout - Black Nitride


AT3 Tactical Standard GI Charging Handle - Black


AT3 20″ 6.5 Grendel Rifle Upper with SPEAR M-LOK Handguard – Made to Order and Ships in 7 Days

AT3 Complete Upper assemblies are Built for Accuracy and Reliability – Guaranteed.

  • Quality Where it Counts – premium components like a Faxon Firearms barrel, adjustable gas block, and AT3 Tactical’s handguards and uppers. Don’t settle for “bargain uppers” with unknown components.
  • Guaranteed Reliability– Carefully assembled before shipment, and backed by the AT3 Lifetime Warranty
  • Unbeatable Value – Unbeatable quality in the price range. Save up to 20% off vs purchasing the components separately.

This fully assembled AR-15 complete upper includes:

20″ Faxon Firearms 1:8 416 Stainless Match Grade Barrel

6.5 Grendel Faxon Firearms Barrel

Faxon Firearms makes some of the finest match-grade barrels in the industry, with precision 5R rifling, polished target crowns, and nickel teflon barrel extensions. The straight fluting keeps this heavy barrel as light as can be, without sacrificing repeatable accuracy, and the QPQ finish offers superior corrosion resistance.

Wojtek Weaponry Adjustable Gas Block

The critical component for the best possible feeding and accuracy on your new upper. Wojtek Weaponry’s adjustable gas blocks are easy to adjust to your favorite factory cartridge or handload, and use a clamp-on design to impart better accuracy better than pinned or set-screw gas blocks.

AT3 SPEAR 15″ Free Float M-LOK handguard

15 inch AT3 Tactical SPEAR Handguard

Unique slim and lightweight design with M-LOK attachment points. Rock-solid 6061 aircraft aluminum handguard that withstands the harshest treatment. 5-slot M-LOK-to-Picatinny rail section included

AT3 Tactical Billet Upper Receiver

AT3 Tactical Billet Upper for AR15

Precision machined from 6061-T6 aluminum, this assembled upper is sleek, with extra material around the barrel extension for superior accuracy. It mates perfectly with our SPEAR handguard and feature M4 feedramps for reliable feeding of ammunition.

Faxon Firearms MUZZLOK 3-Port Brake

This 3-Port Brake uses an innovative design with an integrated jam nut, instead of the common crush washer on most AR15 builds. Not only does the design offer significant recoil reduction, but it is also easy to install and remove depending on your specific application.

Top Add-Ons

AT3 6.5 Grendel Black Nitride Bolt Carrier Group

Finish your complete upper with a reliable, easy to clean Black Nitride Bolt carrier group from AT3. They feature M16 carriers, and MPI inspected bolts made from 9310 steel and properly staked grade 8 gas key screws.

AT3 6.5 Grendel Bolt Carrier Group

Your choice of Standard GI or Extended-Latch Charging Handles from AT3

These 7075-T6 charging handles slide right into our uppers for a complete top end. Choose between a standard latch and extended latch designs to fit your needs and budget.

More info:

This product is built-to-order in our Minnesota facility. Quality takes time – please allow up to 7 days for your order to ship.

All AT3 upper assemblies come with a Lifetime Warranty – if you ever have an issue, let us know, and we’ll make it right. It’s that simple.

Don’t see the options you’re looking for? Let us quote you a custom upper – contact us now.


  • Barrel Length: 20″
  • Total Assembly Length: 26″
  • Gas System: Rifle
  • Barrel Profile: Heavy, Straight Fluted
  • Twist Rate: 1:8
  • Barrel Steel: 416 Stainless Steel
  • Barrel Finish: QPQ Corrosion Resistant (Nitride)
  • Chamber: 6.5 Grendel Type II
  • Muzzle Thread: 5/8×24
  • Barrel Extension: M4
  • Diameter at Gas Block: .750″
  • Gas Block Type: Low-profile
  • Receiver Material: Billet 6061-T6 Aluminum
  • Finish
    • Black: Hardcoat Anodized
    • Flat Dark Earth: H-267 Magpul® Flat Dark Earth
    • OD Green: H-232 Magpul® OD Green
    • Gray: H-188 Magpul® Stealth Grey
    • Pink: H-224 SIG™ Pink
    • Red: H-167 USMC Red
    • Burnt Bronze: H-148 Burnt Bronze
    • Tungsten: H-237 Tungsten
    • Titanium: H-170 Titanium

3 reasons why AT3 Complete Uppers are better than the rest.

1 – Quality Where it Counts

The single most important component of an accurate AR-15 is the barrel. AT3 uppers are built using barrels from top brands like Ballistic Advantage and Faxon Firearms, for excellent performance and accuracy.

But the quality doesn’t stop at the barrel. Our AT3 handguard and upper work together to provide superior accuracy, meaning this upper assembly offers quality without compromises.

Many of the “bargain” complete uppers on the market source their parts from the lowest bidder – at the expense of accuracy and reliable function. AT3 is committed to using only top-quality components in our upper assemblies.

2 – Guaranteed Reliability

AT3 complete uppers are assembled with strict quality controls and carefully packaged for delivery to the customer. All AT3 complete uppers offer a Lifetime Warranty – if you ever have an issue, let us know, and we’ll make it right. It’s that simple.

3 – Unbeatable Value

When you buy a complete upper, you’ll save money and parts and assembly vs purchasing the components separately. Our complete uppers are not the cheapest on the market, but they deliver unbeatable quality in the price range. We sell direct to the customer, and cut out the middle-men, to deliver the best value in AR-15 upper assemblies.

Products available on this page:

Have Questions About this Product?

The AT3 Tactical store has a 90 day no-hassle return policy for products in good condition. You can view the full details of our return policy here.

If you encounter an issue or defect with a product after 90 days of your purchase, you can refer to the manufacturer for a warranty claim. Their policies are below.

AT3 Lifetime Warranty Logo

All AT3 Tactical Brand Products carry a lifetime warranty against manufacturer’s defects.

This includes AT3 Red Dot SightsHandguardsIron Sights, and any other product that carries the “AT3 Tactical” or “AT3™” name. For other brands (ex. Magpul or Troy), please refer to the manufacturer’s warranty policy.

In the event that your AT3™ product becomes unusable, we will repair or replace the product at no charge to you.

If we cannot repair your product, we will replace it with a product in perfect working order of equal or better physical condition. The warranty is fully transferable, but we may require information about the original purchase to validate the authenticity of the product.

If your product is in need of warranty service, please contact AT3 Tactical to start the process

Our contact info is available here. To expedite processing, please provide your order information and description of the defect.

Please note: The AT3 Lifetime Warranty does not cover loss, theft, intentional damage or cosmetic damage that doesn’t affect the performance of the product.

Customer Reviews

Based on 5 reviews
AT3 FF-ML 20 Inch 6.5 Grendel Complete Upper Range Report

Range report, 5 shot group, 1.04 MOA Hornady 123gr ELD Match


Thanks for sharing your feedback, Jim. We're glad you're satisfied with your purchase. Cheers!

adam trost
6.5 20 grendel upper

Gas block was not set up right so rifle would not cycle ammo correctly

Brad Parten
Grendel Build

Just assembled and shot my new Grendel. Functioned great. Waiting on some height specific rings to mount my scope so I can test accuracy.

Thanks for sharing your feedback, Brad. We're glad you're satisfied with your purchase. Cheers!

Completed Build - Extra Upper

Excellent fit and finish. Will test fire/break in, as soon as possible.

Thanks for sharing your feedback, JSP. We're glad you're satisfied with your purchase. Cheers!

Michael Hayes
Grendel Upper

Looks great. Have not had opportunity to shoot it yet. Waiting on other components to complete the build.

Thanks for sharing your feedback, Michael. We're glad you're satisfied with your purchase. - AB