300 Blackout Complete Upper Receivers, Assembled In-House

A 300 Blackout upper should drop onto your existing AR-15 lower and run: no new bolt, no new magazines, no trip to the gunsmith. Every 300 BLK complete upper from AR15Parts.com is assembled, headspaced, and function-checked in-house in Denison, TX, then paired with a barrel, gas system, and twist rate matched to how you plan to shoot it. Backed by 1,700+ five-star reviews and free shipping on orders over $99, we make it easy to get the right upper the first time. Whether you're building a suppressed subsonic rig, a compact pistol upper, or a supersonic hunting upper, call (888) 706-0633 for help choosing the right configuration. Still deciding? Shop our full selection of AR uppers for sale in 19+ calibers.

Build Your 300 BLK Upper

Choose Your 300 Blackout Configuration

AR15Parts.com offers 300 Blackout uppers in 22 configurations rather than one-size-fits-all packages, because the right barrel length, handguard, and muzzle device depend on whether you're running subsonic, supersonic, or a mix of both. 300 BLK performs well from short barrels, so our uppers come in three lengths. Choose from the configurations below, or call our team for help picking the right one.

8" pistol uppers with Ballistic Advantage DRP barrels, the shortest and lightest option for a compact suppressed build
10.5" pistol uppers with Ballistic Advantage DRP Modern Series barrels, a compact, suppressor-ready option with a little more velocity
16" rifle uppers with Wilson Combat, Satern, or AR15Parts.com barrels for maximum supersonic velocity and a non-NFA rifle build
Complete uppers with the BCG and charging handle installed, or the same build without them if you already own a 5.56 BCG
1:7 or 1:8 twist rates that stabilize heavy subsonic projectiles
5/8x24 threaded muzzles ready for a flash hider, brake, or suppressor mount
Gas systems matched to each barrel for reliable suppressed and unsuppressed cycling

Suppressed and Subsonic 300 Blackout Builds

300 Blackout was designed from the ground up for suppressed and short-barreled shooting, which makes a suppressed 300 Blackout upper a natural first build. The cartridge reaches its full ballistic potential from a barrel as short as 9 inches, so a compact 8" or 10.5" upper gives up little of the performance a longer barrel would add, while gaining everything a can and a short gas system bring to handling and sound reduction. Run subsonic 300 BLK loads (typically 190–220 grain) behind a suppressor and the result is remarkably quiet, with reliable cycling when the barrel's gas port and buffer are tuned for it. Switch to supersonic ammunition and the same upper delivers full-power performance for hunting or defense. A 300 Blackout pistol upper on a pistol lower is the most maneuverable version of this platform, ideal for a home-defense or truck-gun role where length matters. Federal rules on pistol braces have changed several times, so check current federal and state laws before building one. Every upper we build ships with a threaded muzzle, a gas system matched to the barrel, and a twist rate that stabilizes heavy subsonic bullets.

Complete Upper vs. Upper Without BCG

Our complete 300 Blackout uppers ship with the bolt carrier group and charging handle installed, so they're ready to run the day they arrive. We also offer the same builds without a BCG and charging handle. Because 300 Blackout uses the same bolt carrier group as 5.56 NATO, many builders already own a compatible BCG and choose this option to save money. Either way, no FFL is required under federal law, so your upper ships directly to your door. Check your state and local laws before ordering.

300 Blackout Upper Compatibility

300 Blackout was built to work with the AR-15 you already own. It uses the same standard bolt carrier group as 5.56 NATO and drops onto any mil-spec AR-15 lower with no modification. Standard AR-15 magazines work, though 300 Blackout-specific magazines with modified feed lips feed more reliably, especially with subsonic ammunition. Here are the key specifications at a glance:

Muzzle Velocity: About 2,200 fps supersonic (125 gr) and about 1,050 fps subsonic (220 gr)
Effective Range: About 300 yards with supersonic loads and 200 yards with subsonic loads
Twist Rate: 1:7 or 1:8
Recoil: Moderate, comparable to 7.62x39
Platform: Standard AR-15 lower receiver

Why Choose AR15Parts.com?

A complete upper is only as good as the assembly behind it, and with 300 Blackout, correct headspacing and a properly tuned gas system are what separate a quiet, reliable suppressor host from a finicky one. Our team assembles every upper in-house at our Denison, TX facility and stocks barrels from vetted manufacturers so each build matches its intended use. Here's what builders gain when ordering through us:

Trusted Barrel Makers: Wilson Combat, Ballistic Advantage, and Satern barrels are stocked alongside AR15Parts.com barrels, so you can match profile, length, and twist to subsonic or supersonic use.
In-House Assembly and Headspace Verification: Every upper is assembled, headspaced, and function-checked before it ships, which is critical for a caliber run heavily suppressed.
22 Configurations to Choose From: Pick from 8", 10.5", or 16" barrels, 10", 12", or 15" handguards, an A2, flash can, or comp brake muzzle device, and builds with or without the BCG and charging handle installed.
Fast, Free Shipping: Most in-stock configurations ship within 3–5 business days, and orders over $99 ship free.
1,700+ Five-Star Reviews: Builders across the country trust AR15Parts.com for their uppers, parts, and customer service.

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300 Blackout Uppers Built for Every Mission

The 300 Blackout's versatility across subsonic and supersonic loads is exactly why builders choose a caliber-specific complete upper instead of settling for a factory rifle. Here are the most common applications builders choose 300 BLK uppers for:

Suppressed home-defense carbines and pistols
Subsonic suppressor hosts for low-noise range and backyard shooting
Short-barreled pistol (PDW) and SBR builds where length matters (an SBR still requires NFA registration, even though the tax stamp has been $0 since January 2026)
Hog and predator hunting with supersonic loads
Suppressed hunting rigs with threaded, gas-tuned barrels
Truck guns, pack guns, and lightweight backcountry builds
Range and training uppers for high-volume shooting

See What Our Customers Have to Say

Build Your 300 Blackout Upper Today

Choosing the right 300 Blackout configuration isn't always obvious. Subsonic-only, supersonic-only, and mixed-use builds each favor different barrel and gas combinations. The AR15Parts.com team can walk through barrel length, gas system pairing, twist rate, and suppressor compatibility before you commit. Every upper is headspaced and function-checked before it ships.

Contact AR15Parts.com to start your build, or call (888) 706-0633 to speak with a builder directly.

Frequently Asked Questions

Will a 300 Blackout upper work on my existing AR-15 lower?

Yes. The 300 Blackout was designed to run on a standard AR-15/M4 lower using the same 5.56/.223 bolt carrier group and standard AR-15 magazines. Drop the assembled upper onto your lower and you're ready to go, with no proprietary parts required.

What barrel length is best for a 300 Blackout upper?

300 BLK reaches its designed performance from barrels as short as 9 inches, which makes our 8" and 10.5" uppers a strong fit for suppressed and pistol builds. A 16" barrel squeezes out the most supersonic velocity and keeps the rifle non-NFA. If you'll shoot mostly subsonic and suppressed, choose 8" or 10.5". If you want maximum supersonic reach, choose 16".

Can I shoot both subsonic and supersonic ammo through the same upper?

Yes. A properly configured 300 Blackout upper cycles both. Subsonic loads (typically 190–220 gr) shine behind a suppressor for quiet shooting, while supersonic loads (typically 110–150 gr) deliver full-power performance for hunting and defense. Each barrel's gas system is matched for reliable cycling, and our team can help you pick the right upper for the loads you plan to use.

Is 300 Blackout good for suppressed shooting?

It's one of the best AR-15 calibers for it. The cartridge was engineered around short barrels and subsonic performance, so a suppressed 300 Blackout upper stays compact and quiet without sacrificing reliability. Our barrels come threaded 5/8x24, and we match the gas system for consistent cycling with a can attached.

What twist rate do I need for 300 Blackout?

A 1:7 or 1:8 twist is standard for 300 BLK because it stabilizes the heavy subsonic bullets the caliber is known for while still handling lighter supersonic loads. Every 300 Blackout barrel we stock uses a twist rate appropriate for the full range of factory ammunition.

Do I need an FFL to buy a 300 Blackout upper?

No, not under federal law. The upper isn't the serialized part of an AR-15, so it ships directly to your door. Some states and cities have their own rules, so check your local laws before ordering.

What is the effective range of 300 Blackout?

With supersonic ammunition, 300 Blackout is effective to about 300 yards. Subsonic ammunition is practical to about 200 yards. For longer-range needs, consider .223 Wylde or 6.5 Grendel.

Is 300 Blackout good for deer hunting?

Yes. With supersonic 110–150 gr hunting loads, 300 Blackout is effective on whitetail deer within 200 yards. It's especially popular for hog hunting.

How long does shipping take?

Most in-stock configurations ship within 3–5 business days, and custom builds may take 2–3 weeks. Orders over $99 ship free.

Is it dangerous to mix 300 Blackout and 5.56 ammunition?

Yes, and this is the one safety rule every 300 BLK owner must know. A 300 Blackout round can chamber in a 5.56/.223 barrel and cause a catastrophic failure if fired. Keep your 300 BLK ammunition clearly separated from your 5.56, mark your 300 BLK magazines, and never load 300 Blackout into a rifle chambered in 5.56.