ATI Mil Sport AR-15 Stripped Lower Flat Cobalt Cerakote, Multi Cal

The ATI Mil Sport AR-15 Stripped Lower Flat Cobalt Cerakote, Multi Cal is a foundational component for shooters across the United States who are building a rifle that fits their specific needs—whether that means a lightweight varmint setup for the Texas plains, a reliable home defense carbine for a suburban family, or a cost-effective target rifle for weekend range trips. As a stripped lower receiver, it serves as the legal firearm component of your build, giving you the flexibility to choose every other part according to your preferences and budget. This particular model from American Tactical Imports (ATI) combines a durable Cobalt Cerakote finish with a flat dark earth-inspired aesthetic, making it a practical starting point for a wide range of AR-15 platforms.

What This Product Is and Who It’s For

This is a stripped lower receiver for the AR-15 platform, meaning it is the serialized core of the firearm that you will build upon with your choice of upper receiver, barrel, stock, and fire control group. It is intended for individuals who want to assemble their own rifle rather than purchase a complete firearm, offering the ability to tailor caliber, barrel length, handguard, and accessories to specific tasks. This product is well-suited for target shooters who enjoy precision work at the range, home defense users who prioritize a custom fit and reliable function, hunters who need a lightweight and modular platform for medium game, and collectors who appreciate the unique Cobalt Cerakote finish. It is not a complete rifle; it requires assembly by the buyer or a qualified gunsmith.

Key Spec Breakdown

• Caliber: Multi-caliber compatible (223 Remington, 5.56x45mm NATO, 300 Blackout, and other AR-15 compatible cartridges).
• Receiver Material: 7075-T6 aluminum, a standard for durability and weight savings.
• Finish: Flat Cobalt Cerakote, a baked-on ceramic coating that resists corrosion, scratches, and wear.
• Weight: Approximately 0.8 pounds (12.8 ounces) as a stripped lower, depending on exact machining.
• Trigger Guard: Integrated, standard mil-spec design.
• Grip: Not included; this is a stripped receiver with no grip or stock.
• Stock: Not included; requires a buffer tube and stock of your choice.
• Sights: Not included; lower receiver does not include sights.
• Capacity: Magazine-fed; standard capacity depends on your chosen magazine (typically 10, 20, or 30 rounds for 5.56mm).
• Barrel Length: Not applicable; barrel is not included with this stripped lower.
• Overall Length: Not applicable until assembled with a stock and barrel.
• Safety: Standard mil-spec safety selector pocket; safety not included.
• Manufacturer: ATI American Tactical Imports.
• SKU: 819644020073.
• UPC: 819644020073.
• Classification: Firearm (receiver).

Feature Deep-Dive

The ATI Mil Sport AR-15 Stripped Lower is machined from 7075-T6 aluminum, which is a heat-treated alloy known for its strength-to-weight ratio. This material is the industry standard for AR-15 lower receivers because it offers reliable structural integrity without adding unnecessary weight to your build. The forging process used by ATI produces a receiver that meets mil-spec dimensions, ensuring compatibility with a wide range of upper receivers, buffer tubes, and aftermarket parts. This consistency is important for builders who want to avoid fitment issues during assembly, particularly when combining parts from different manufacturers. The receiver is also hard-coat anodized under the Cerakote finish, providing an additional layer of protection against oxidation and wear.

The Flat Cobalt Cerakote finish is a key feature of this model. Cerakote is a ceramic-based coating that is applied as a thin layer and then cured, creating a surface that is more resistant to scratches, solvents, and impact than standard anodizing. The flat finish reduces glare, which can be an advantage in low-light conditions or when shooting from a prone position. The Cobalt color is a medium blue-gray tone that pairs well with black, FDE, or gray furniture, offering a subtle customization option without being overly tactical. This finish is also easy to clean, as it resists carbon buildup and can be wiped down with standard gun cleaning solvents without damaging the coating.

ATI has designed this lower with an integrated trigger guard, which eliminates a potential point of failure and simplifies assembly. The trigger guard is wide enough to accommodate gloved fingers, a practical consideration for shooters in colder climates or those who wear tactical gloves during training. The magazine well is flared slightly to facilitate faster reloads, though the flare is subtle enough to remain compatible with standard AR-15 magazines. The receiver is also compatible with both mil-spec and enhanced trigger groups, allowing you to choose a trigger that matches your intended use—whether that is a crisp single-stage for target shooting or a two-stage for precision work.

The lower receiver includes standard markings for safety selector positions (Safe, Semi, and Auto, though the auto position is not functional on a semi-automatic build) and is drilled for a standard rear takedown pin detent. The pocket for the fire control group is machined to accept drop-in triggers as well as standard mil-spec parts, giving you flexibility in your build. The bolt catch and magazine catch are not included but are standard mil-spec size, so you can source them from any reputable manufacturer. The receiver extension (buffer tube) threads are also mil-spec, ensuring that you can attach a standard carbine or rifle buffer tube without modification.

One practical advantage of this stripped lower is its compatibility with multiple calibers. While the AR-15 platform is most commonly associated with 5.56x45mm and .223 Remington, this receiver can also be used with 300 Blackout, 9mm (with a dedicated magazine adapter), 22 LR (with a conversion kit), and other cartridges that fit within the AR-15 magazine well. This makes the receiver a versatile foundation for a single build that can be reconfigured for different roles—for example, using a 5.56 upper for varmint hunting and a 300 Blackout upper for suppressed home defense. The multi-caliber designation also means you are not locked into a single cartridge, which can be useful if you want to experiment with different loads or calibers over time.

The receiver is also designed to be compatible with a wide range of aftermarket accessories. The rear of the receiver includes a standard buffer tube mount, which accepts any mil-spec or commercial-spec buffer tube (though mil-spec is recommended for consistency). The trigger guard area is clear of obstructions, so you can install ambidextrous safety selectors, bolt releases, or magazine releases if desired. The receiver also has standard threaded holes for a rear takedown pin detent and a spring, as well as a hole for the bolt catch roll pin. All of these features are machined to standard tolerances, meaning you can use parts from brands like Aero Precision, Magpul, BCM, or Geissele without modification.

Ideal Use Cases

This stripped lower is best suited for range shooting, where you can build a rifle optimized for accuracy and reliability with a free-floating barrel and a match-grade trigger. It also works well for home defense, as the Cerakote finish is durable enough to withstand repeated handling and the receiver can be paired with a short-barreled upper (with proper NFA paperwork) or a standard 16-inch barrel. For hunting, the receiver’s lightweight aluminum construction is an advantage when carrying a rifle through brush or over uneven terrain, and the multi-caliber compatibility allows you to choose a cartridge appropriate for deer, hogs, or predators. Collectors may find the Flat Cobalt color a distinctive addition to a safe, particularly when paired with matching Cerakote accessories. This product is not intended for concealed carry due to its size and the requirement for assembly into a full rifle.

Compatibility Notes

• Ammunition: Compatible with 223 Remington, 5.56x45mm NATO, and 300 Blackout ammunition, as well as other AR-15 compatible cartridges when using the appropriate upper and magazine.
• Holsters: Not applicable; this is a receiver, not a handgun. Holsters are not used with this product.
• Magazines: Accepts standard AR-15/M16 magazines in 223/5.56, 300 Blackout, 9mm (with adapter), 22 LR (with conversion), and other compatible magazine types.
• Accessories: Compatible with mil-spec buffer tubes, trigger groups, pistol grips, and stocks from most manufacturers. Aftermarket safety selectors, bolt catches, and magazine releases should be standard mil-spec size.
• Upper Receivers: Works with any mil-spec AR-15 upper receiver, including flat-top, carry handle, and side-charging models.

FAQ Section

1. How does shipping to my U.S. address work for this product?
This product is a firearm (stripped lower receiver) and can only be shipped to a Federal Firearms License (FFL) holder in your state. We do not ship directly to residential addresses. After you place your order, we will require the FFL’s contact information and a copy of their license. We will then ship the receiver to that FFL, where you can complete the transfer after passing a background check. Shipping is available to all U.S. states where AR-15 lower receivers are legal, subject to state and local laws.

2. What is the FFL transfer process?
Once your order is placed, you will need to provide the name, address, and phone number of a licensed FFL dealer in your area who is willing to process the transfer. We will ship the receiver to that dealer. You will then visit the dealer to fill out ATF Form 4473 and undergo a background check (NICS). Once approved, the dealer will release the receiver to you. Transfer fees vary by dealer and are not included in the purchase price. We recommend contacting your chosen FFL before ordering to confirm they accept shipments from online retailers.

3. What ammunition is compatible with this receiver after assembly?
This stripped lower is compatible with any cartridge that fits the AR-15 platform. For 5.56x45mm and .223 Remington, use standard AR-15 magazines. For 300 Blackout, use the same magazines (though dedicated 300 Blackout magazines can improve reliability with subsonic loads). For 9mm, a dedicated magazine adapter and 9mm upper are required. For 22 LR, a conversion bolt and magazine are needed. Always verify that your complete build’s barrel and chamber match the ammunition you intend to use.