Built for short barrels and suppressors. NSPEC Innovations carries the 300 Blackout parts that convert an AR-15 into a compact, quiet .30-caliber platform: complete uppers, heavy barrels, multi-caliber bolt carrier groups and 5/8x24 muzzle devices. Swap a barrel, keep your lower, and run subsonic suppressed or supersonic loud.
300 Blackout was engineered by Advanced Armament Corp to give the AR-15 a .30-caliber round that burns fully in a short barrel and runs quiet when suppressed. It reaches full powder burn around 9 inches, matches the muzzle energy of a 16-inch 5.56 from a 10.5-inch barrel, and feeds from standard AR-15 magazines. Here is where it shines.
Subsonic loads stay below the sound barrier, so a suppressor makes them genuinely quiet with no supersonic crack. This is the reason the cartridge exists.
Full performance from a short barrel makes 300 BLK ideal for AR pistols and SBRs, where 5.56 loses most of its velocity advantage.
.30-caliber terminal energy up close suits hogs and deer inside 150 yards and home-defense use, with manageable recoil.
300 Blackout was designed to reuse the AR-15 platform. To convert an existing 5.56 rifle you change the barrel and gas system, and everything else carries over. Start with a complete upper for the easiest path, or build from a barrel up.
The fastest route. A complete 300 BLK upper arrives assembled with the correct barrel and pistol-length gas system, and pins onto any mil-spec lower. Our 10.5-inch upper hits the cartridge's sweet spot.
Building your own upper starts here. A 300 BLK barrel is one of only two caliber-specific parts. Our 16-inch heavy barrel suits range and hunting use where you want a full-size profile.
A standard AR-15 BCG runs 300 BLK. Our multi-caliber side-charging BCGs cover .223, 5.56, .300 BLK, .223 Wylde and .350 Legend, in nitride or nickel boron, so one bolt serves several uppers.
300 BLK barrels use a 5/8x24 thread. Cap it with a brake or comp, or a suppressor mount if you are running a can. Our 5/8x24 breacher compensator fits the .30-caliber thread.
Your existing lower, buffer, magazines and handguard all carry over from a 5.56 build, which is what makes a 300 Blackout conversion so quick and affordable.
Because 300 Blackout and 5.56 share the same parent case, a 300 BLK round will chamber in a 5.56 barrel. When fired, the .30-caliber bullet cannot pass through the .224 bore. The result is a catastrophic failure that can destroy the rifle and cause serious injury.
Keep 300 BLK and 5.56 ammunition and magazines physically separated. Color-code or clearly mark every 300 Blackout magazine, and never load 300 BLK into a magazine you also use for 5.56. This one habit prevents the most dangerous mistake in the platform.
Because the cartridge burns fully in a short barrel, you are not penalized for going short the way you are with 5.56. Match length to how you shoot.
Dedicated suppressed subsonic. The shortest, lightest builds for AR pistols and SBRs run quiet with subsonic ammo and a can. Supersonic velocity drops off more at these lengths.
The all-round sweet spot. Recovers about 92 percent of the supersonic velocity of a 16-inch barrel and cycles both subsonic and supersonic loads reliably. The best single choice for most builders.
Range, hunting and simple compliance. A full rifle-length profile for unsuppressed use. Little velocity gain over 10.5 inches, but no SBR or pistol considerations.
Use a pistol-length gas system, even on a 16-inch barrel, for the most consistent cycling across subsonic and supersonic. Add an adjustable gas block if you plan to run suppressed and switch loads often.
300 Blackout was designed to reuse almost all standard AR-15 parts. To convert an existing 5.56 rifle you typically change only two things: the barrel and the gas system. A 300 BLK barrel (pistol-length gas is standard), a standard AR-15 bolt carrier group, your existing lower, standard magazines and a suppressor-ready muzzle device complete the build. The fastest path is a complete 300 BLK upper that pins onto any mil-spec lower.
A 300 Blackout round will chamber in a 5.56 barrel because both cartridges share the same parent case, but firing it causes a catastrophic failure that can destroy the rifle and cause serious injury. The .30-caliber bullet cannot pass through the .224 bore. Always keep 300 BLK and 5.56 ammunition and magazines physically separated, and color-code or clearly mark every 300 BLK magazine.
Yes. A standard AR-15 bolt carrier group works with 300 Blackout, your existing mil-spec lower works, and standard AR-15 magazines feed 300 BLK at full capacity with no modification. That shared compatibility is a core reason the cartridge is so easy and affordable to build. Only the barrel and gas system are caliber-specific.
For most builders, 10.5 inches is the sweet spot. It recovers roughly 92 percent of the supersonic velocity of a 16-inch barrel in a much shorter package and cycles both supersonic and subsonic loads reliably. Dedicated suppressed subsonic builds often use 7 to 9 inches, while 16 inches suits unsuppressed range use and simpler rifle-length compliance.
Nearly all 300 Blackout builds use a pistol-length gas system, even on 16-inch barrels, because it provides the most consistent cycling with both subsonic and supersonic ammunition. A carbine or longer gas system may fail to cycle subsonic loads reliably. If you plan to run a suppressor and switch between subsonic and supersonic, an adjustable gas block helps you tune the rifle.
Neither is better overall; they solve different problems. Choose 300 Blackout for suppressed shooting with subsonic ammo, short-barrel pistol and SBR builds, and close-range hunting or home defense, where it delivers .30-caliber energy from a short barrel. Choose 5.56 for longer range, flatter trajectory and lower ammo cost. Many shooters keep one lower and swap uppers between the two.
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