One of the advantages of the AR-15 rifle pattern is its modularity. There is a seemingly endless supply of interchangeable drop-in parts and assemblies for the hobbyist or gunsmith who builds rifles. And one of the most popular builds as of late is the .300 Blackout AR-15 build.
Best .300 Blackout Lower Receivers
For a .300 Blackout rifle build, a receiver designed for a 5.56mm AR-15 is sufficient. Just replace the bolt carrier group.
PSA AR-15 Complete Lower Magpul MOE Edition
PSA (Palmetto State Armory) offers several options for the beginner or budget-conscious hobbyist. If all you want is an entry-level lower or intend to replace the pistol grip and butt stock immediately, the Classic Stealth Lower may be the better choice. However, if you’d like to start your build with a pistol grip and a butt stock that you’d like to keep, the Magpul MOE (Magpul Original Equipment) Edition is probably more your speed. Both products are mil-spec, but the MOE Edition is an upgrade.
The MOE Carbine Stock provides at least 2 noticeable advantages relative to the M4. For one, the release latch, which you press to collapse or extend the stock, is protected against unintentional activation. Another is that the butt pad is 0.30” non-slip rubber, providing both cushioning for the shoulder and a more grip-like texture.
The MOE pistol grip represents an ergonomic improvement relative to the standard A2/M4 variant. A more hand-filling design, the MOE pistol grip has a beavertail backstrap that covers part of the lower receiver, allowing you to achieve a higher hand position for increased control of the weapon. While the MOE pistol grip comes with a simple grip cap, it does accept storage cores that you can use to keep anything from spare batteries to a few extra rounds of ammunition available.
Anderson Manufacturing AM-15 80% Lower Receiver
The second item on the list is an 80% lower receiver made by Anderson Manufacturing. Perhaps best known for its RF-85 corrosion- and wear-resistant surface treatment, Anderson has also been producing inexpensive AR-15-pattern rifles and spare parts for years.
There has been significant controversy surrounding the topic of 80% lower receivers, some calling them “ghost guns” because of their apparent lack of traceability.
The AM-15 80% lower receiver here is black anodized, so after milling the pocket for the fire control group, you’ll have to decide whether you want to leave the pocket bare aluminum or have it re-anodized. There are bare aluminum options available as well, but you’ll still need to anodize them afterward.
Although Anderson has not performed the most critical machining operations, so you’ll have to put the work in, the exterior has been profiled. The holes for the takedown pins and trigger guard, the slots for the magazine catch/release and bolt/catch release, and all necessary fencing. However, the lower also includes 2 stops for the safety selector lever on the left side.
James Madison Tactical Gen 2 Polymer 80
Most 80% lower receivers, or receiver blanks, are made from aluminum, either a machined forging or machined from billet. Some are investment cast, although this is rare. However, what’s even less common is an 80% lower receiver made from injection-molded polymer composite.
Representing a significant weight saving relative to aluminum, the Polymer 80 has another notable advantage — it’s easier to machine. If you’re new to milling gun parts, machining polymer is less strenuous on tools, increasing the life of both drill bits and milling cutters.
When milling an 80% aluminum receiver, you have 2 choices. You can buy an already anodized blank and remove the anodizing where you have to mill the fire control group pocket and drill the horizontal holes. Alternatively, you can purchase a bare aluminum blank and anodize it after machining. That is, if you want it to be black.
If you don’t, then it doesn’t matter. It’s the same color after machining with polymer as it was when it arrived at your door. No additional surface finishes or treatments are necessary, and polymers can’t corrode or rust. You have 4 colors to choose from — black, wolf grey, flat dark earth, and olive drab.
JMT has designed the 80% Polymer Lower to comply with mil-spec dimensions, so you’ll be able to install drop-in parts.
Milling an 80% may be a daunting task for some, but JMT makes this a straightforward affair. The company includes a 3-piece jig to help you guide you through the machining process.
Sharps Bros Warthog AR-15 Stripped Lower
Sharps Bros is taking a fresh approach to the AR-15 parts market, manufacturing unorthodox and ornately styled multi-caliber lower receivers to draw attention.
Offering several options, from skulls to Spartan helmets, this lower is inspired by the Warthog, the affectionate nickname assigned to the A-10 Thunderbolt II. Now, a 30mm GAU-8 Avenger cannon is a far cry from an AR-15.
A multi-caliber stripped lower receiver, this has been machined to completion by Sharps for you but contains no component parts. A good starting point for the builder who wants to assemble a rifle but either can’t machine it himself or doesn’t want to. The hole for the safety selector lever features pictogram markings for safe and fire.
The Warthog, which is machined from 7075-T6 aluminum, is fully compatible with mil-spec parts and assemblies, and can accept USGI or Magpul magazines. As the .300 Blackout shares the same lower receiver with the .223/5.56mm cartridge, you’re also able to match the Warthog with any mil-spec upper receiver.
Featuring an oversized integral trigger guard for use with gloves and a beveled and flared magazine well for smooth reloads, the Warthog is an excellent stripped lower for the AR-15 builder who wants their rifle to stand out.
BAD BAD556-LW Lightweight Stripped Lower Receiver
If you’d like to begin your build with a lightweight stripped lower, the BAD556-LW, made by Battle Arms Development, weighs a mere 6.84 oz. This is thanks to some creative lightening cuts and other milling operations. You’ll notice the magazine well immediately.
However, don’t miss the face milling that has removed material from the sides of the receiver. The holes and slots for pins and other parts are raised. An added benefit is that the safety selector hole has a relief cut to accommodate the short-throw BAD selector lever. To help you keep your index finger off the magazine release until you need to, there is more prominent fencing around the release button.
CNC machined from a 7075-T6 aluminum billet, the lower is Type III hard-coat anodized black, per military specifications, and features an oversized integral trigger guard. As noted, the magazine well features a rather elaborate design, but it’s not skin deep — it’s beveled and flared for rapid magazine changes.
Inspected for dimensional accuracy, the BAD lower is mil-spec compatible, so any drop-in part or assembly you buy is sure to fit. If you’re worried about sharp edges from machining, BAD’s team carefully deburrs every receiver by hand. Laser engraved, the company logo, and multi-caliber markings deeply so you’re not likely to miss them.
PSA Complete Rifle Lower Receiver A2
When you want to get back to basics, PSA offers a complete lower receiver with an A2 pistol grip and fixed stock. If you’re interested in building a semi-automatic reproduction of an M16A2 rifle but prefer the performance of the .300 Blackout cartridge, this lower receiver package should serve you well.
Many shooters see the fixed A2 stock as antiquated. It doesn’t offer length-of-pull adjustable, for example, and it’s heavier than the collapsible varieties. However, the increased rigidity of a fixed stock does provide at least 2 advantages relative to collapsible.
If you need to clear a malfunction by slamming the butt against a hard surface, the fixed stock can withstand that impact better than many collapsible types. If you ever need to use your rifle’s stock as a blunt instrument, especially as a striking weapon, fixed is the superior choice.
The A2 pistol grip is standard, but if you handled an M16 or M4 in the service, you might appreciate the familiarity. If not, it’s easily replaceable.
For a .300 Blackout rifle build, most of what’s included is compatible; however, you may want to pay careful attention to the buffer assembly. The fixed A2 stock contains a rifle-length buffer and recoil spring.
While there’s some debate regarding the most appropriate gas system to choose for optimal performance with this cartridge, shooters often find that pistol-length gas systems are the most versatile, allowing the reliable use of comparatively low-pressure subsonic loads. The gas system works alongside the buffer, so you must investigate this topic to determine which combination will work best for your preferred barrel length and loads.
Seekins Precision NX15 Billet AR-15 Lower Receiver
Another lightweight lower receiver, this one can be considered a hybrid. Fully machined from a 7075-T6 aluminum billet, the NX15 is technically a stripped lower, so there is no fire control group, and most of the other component parts are missing.
There is a prominent bolt catch/release lever on the left side, which takes the form of an oversized and textured paddle for easy access. On the right side of the receiver, above the slot for the magazine release, is the companion — a bolt release you can press with your right index finger.
This lower should accommodate the left- or right-handed shooter interested in building an ambidextrous rifle for competitive target shooting or self-defense.
It’s also for the builder who wants to keep weight to a minimum. Thanks to extensive skeletonizing, Seekins has managed to keep the weight to a modest 9.45 oz. This also serves to stylize the lower, ensuring that your AR-15 build truly stands out from the rest.
As with some of the other lowers on the list, the trigger guard is integral and winterized, meaning that it’s oversized to allow your use of warm winter gloves. The NX15 also features pictogram safety selector roll marks, and the front of the magazine well has been milled for additional texture. So if you grip the front of the lower for support, your hand is less likely to slip off.
If you’re interested in assembling your AR-15, you have three lower-receiver options:
- 80%: Also known as a receiver blank, an 80% lower receiver has not been fully machined by the manufacturer. The manufacturer will usually have machined the exterior profile, the slots for the magazine catch/release, bolt catch/release, drilled the holes for the takedown pins and trigger guard, etc. However, you will have to mill the pocket for the fire control group yourself.
- Stripped: The next option is the stripped lower receiver. This has been machined to completion and constitutes a firearm legally but contains no component parts, so you’ll need to buy a lower parts kit (LPK) to render it functional.
- Complete: This is the complete lower receiver. Machined to completion and including all necessary component parts, such as the fire control group, magazine catch, bolt catch, and all related springs, pins, and detents.
The .300 Blackout was developed by AAC (Advanced Armament Corporation) in response to the need for a SAAMI-standardized cartridge, compatible with the AR-15 rifle platform, that could outperform the 5.56mm and 7.62×39mm cartridges when fired from carbine- or Commando-length barrels.
Furthermore, the .300 Blackout, when loaded subsonic, works exceptionally well with a sound suppressor (silencer) and packs more punch than a 9mm submachine gun.
As you can use a standard 5.56mm bolt carrier group and a USGI magazine with the Blackout, there’s no need for a specialty AR-15 rifle.
The lower receiver of the AR-15 is legally the firearm — no other component or assembly qualifies. However, a receiver blank, called an 80% lower, is not regulated by the ATF so that you can machine it to completion.
Remember, however, to familiarize yourself with your local state laws. For example, California requires you to include a serial number on the receiver blank before you finish it. Other states have other restrictions, such as New Jersey, which does not allow residents to sell receiver blanks.
Several options are available if you’re building a .300 Blackout rifle, whether for work, competition, or recreation. The option you choose depends on your personal operational preferences.