AT3™ AT-15 FLATLINE Rifle 16 Inch 5.56 NATO - 15 Inch M-LOK Handguard
or 4 interest-free payments of $275.00 with 
This item is regulated, therefore your entire order will be shipped to an FFL dealer of your choosing. After you place your order, we will contact you to finalize these details.
6 Magazines Per Order: Due to extreme volume, we are limiting sales of magazines to 6 per customer order. This applies to individual and bundled magazines. AT3 reserves the right to cancel any order over the 6 magazine limit.
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- Backed by the AT3 Lifetime Warranty! what it covers
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Product description
AT3 Tactical FLATLINE 5.56 Rifle – the AR You Wanted the First Time
The FLATLINE 5.56 rifle has all the features you need, plus the bells and whistles you’ll actually want in an AR-15. For years, we’ve helped folks upgrade or build their custom rifles, and now we’re offering this: a rifle that does everything you ask, equipped with great components you’ll want to keep. Plus, three great matching finishes to suit your preferences.
We want you to hit the range running with the FLATLINE. This rifle comes equipped with a free floating 15 inch M-LOK handguard, ambidextrous charging handle, mag catch, and safety, a 4.5 pound single stage trigger, and Magpul furniture for a comfortable, modernized feel. Grab an optic, load up your color-matched magazine, and get ready to send it.
Be sure to check out our Red Dot Sights and Scopes to make this rifle complete and ready for the range. For home defense, we always recommend a Weapon Light to identify your targets, as well as a Sling for weapon retention under stress. To improve your grip, consider a Front Grip for the handguard, or a Bipod for greater stability.
For the AT3 Team’s curated upgrade picks check them out at our AT3 FLATLINE Upgrade Page!
A Go Everywhere, Do Everything Rifle
- Single Stage, 4.5 Pound Trigger by Alex Pro Firearms Performs in Competition, Duty, and Self-Defense Roles
- Government Profile Barrel Ensures Accuracy Under Heavy Use, and Easy Supports a Suppressor
- 15 Inch M-LOK Handguard Makes it Simple to Mount Foregrips, Bipods, Lights, Lasers, and More
- 4 Port Combat Flash Hider Easily Mitigates Recoil and Reduces Flash Signature
All the Bells and Whistles
- Breek Warhammer Charging Handle for Fast, Smooth Charging in Any Scenario
- Magpul K2 Grip and DT Carbine Stock for Comfortable, Modernized Weapon Handling
- Magpul ASAP QD Endplate for Easily Mounting Single or Two-Point Slings
- Ambidextrous Safety and Magazine Release for Complete Control in Dynamic Environments
Available Finishes
- Black: Type 3 Hardcoat Anodized
- Flat Dark Earth: H-267 Magpul® Flat Dark Earth
- OD Green: H-232 Magpul® OD Green
What’s Included
- AT3 AT-15 Receiver Set
- AT3 SPEAR 15 Inch M-LOK Handguard
- AT3 Black Nitride Bolt Carrier Group
- Magpul M2 30 Round PMAG – Color Matched for Cerakote Rifles
- Alex Pro Firearms 4.5 Pound Single Stage Trigger
- Magpul DT Carbine Stock
- Magpul K2 Pistol Grip
- Breek Arms Warhammer Charging Handle
- Arms Unlimited Ambidextrous Magazine Catch
- AT3 Ambidextrous Safety Selector
Specifications
- Platform: AR-15
- Made In America: Yes
- Caliber: .223 Remington/5.56 NATO
- Barrel Length: 16″
- Barrel Thread Pitch: 1/2×28
- Barrel Twist Rate: 1/7
- Barrel Profile: Government
- Barrel Material: 4150 CMV Steel
- Bolt Material: 9310 Steel (MPI Inspected)
- Gas System: Mid-Length Direct Impingement
- Ambidextrous: Yes
- Rail Attachment: M-LOK
- Free-Float: Yes
- Trigger: Single Stage, 4.5 Pound Pull Weight
FAQ
What is Cerakote?
Cerakote is a ceramic paint and adheres to polymer and metal very well. Since the the lowers are painted, some wear marks may be seen on areas of heavy use. AT3 doesn’t warranty against Cerakote inconsistencies or the wearing of coatings. Our parts are Cerakoted using the official Cerakote colors.
All 3 options on this page
- AT3™ AT-15 FLATLINE Rifle 16 Inch 5.56 NATO - 15 Inch M-LOK Handguard - Color: Black SKU AT3-FLATLINE-556-BLK · UPC 5060748424266
- AT3™ AT-15 FLATLINE Rifle 16 Inch 5.56 NATO - 15 Inch M-LOK Handguard - Color: Flat Dark Earth SKU AT3-FLATLINE-556-FDE · UPC 5060748424273
- AT3™ AT-15 FLATLINE Rifle 16 Inch 5.56 NATO - 15 Inch M-LOK Handguard - Color: OD Green SKU AT3-FLATLINE-556-ODG · UPC 5060748424280
Customer reviews 1
Verified buyer Questions & Answers 2
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Are these barrels equipped to fit an suppressor from factory or would I need an adaptor kit or something else? Thanks.
Mitchell · Mar 15, 2026AT3 Support Team — Yes, the AT3 AT-15 FLATLINE Rifle's 16" 5.56 barrel is equipped for suppressors from the factory—no adapter kit or modifications needed.
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Is there an YouTube video for this rifle , accuracy at 100, or ammo that might perform well with? I'm looking for a mid tier rifle and this looks good but would like more information. Rifle sku: AT3-FLATLINE-556-FDE
Vic · Jan 23, 2025AT3 Support Team — Thanks for reaching out, There is not yet but we are working on this Thanks
Warranty & returns
Backed by the AT3 Lifetime Warranty!
All AT3 Tactical Brand Products carry a lifetime warranty against manufacturer’s defects.
This includes AT3 Red Dot Sights, Handguards, Iron 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.
