300 Blackout Ammo

.300 Blackout (300 BLK) is an AR-15 cartridge designed by Advanced Armament Corporation and Remington Defense to deliver rifle-caliber performance in a suppressed SBR platform — using the same bolt, carrier, and magazines as a 5.56 AR-15 with only a barrel change. Its ability to run both supersonic hunting loads and hearing-safe subsonic suppressor loads from the same platform makes it one of the most versatile cartridges in the AR-15 ecosystem. Impact Guns carries .300 Blackout in supersonic, subsonic, and hunting configurations from all major manufacturers.

Read our full .300 Blackout Ammunition Buying Guide ↓

.300 Blackout Ammunition Buying Guide

Supersonic vs. Subsonic: The .300 Blackout Advantage

.300 Blackout uniquely offers two completely different performance profiles in the same platform. Supersonic loads (110–125 grain at 2,100–2,350 fps) deliver .30-30-class energy for hunting and general-purpose use with a significant velocity advantage over pistol calibers. Subsonic loads (190–220 grain at 1,000–1,050 fps) reduce noise substantially when used with a suppressor — producing energy comparable to .45 ACP from the same rifle. Both load types cycle the same AR-15 action reliably with an appropriate gas system. This dual-mode capability is the core design feature that distinguishes .300 Blackout from every other AR-15 caliber.

Suppressor Use: The Primary Use Case

.300 Blackout in subsonic configuration with a suppressor is one of the quietest centerfire rifle setups available. Subsonic loads eliminate the supersonic crack; the suppressor handles the muzzle blast. From a 9-inch SBR barrel with a quality suppressor, the result is hearing-safe for most shooters without additional protection. Federal 220gr Open Tip, Hornady 208gr A-MAX Subsonic, and Remington 220gr OTM are reliable suppressor loads that cycle AR-15 actions consistently. Since January 1, 2026, the NFA tax stamp has been eliminated — see our suppressors page and ATF eForms guide for the registration process.

Barrel Length Guide: Short vs. Standard

Barrel length significantly affects .300 Blackout performance. A 9-inch barrel is the sweet spot for suppressed subsonic builds — short enough for extreme compactness, and subsonic loads don't benefit meaningfully from longer barrels. For supersonic loads, a 16-inch barrel extracts full velocity from the cartridge and keeps the build as a legal rifle without NFA registration. An 8-10-inch barrel with supersonic loads loses meaningful velocity versus 16 inches, but many SBR builders accept that tradeoff for compact overall length. For an unsuppressed hunting or general-purpose build, 16 inches is the right length. For a suppressed SBR, 9–10 inches is the most common configuration.

Hunting Loads

Supersonic .300 Blackout loads are capable of taking deer, hogs, and similar game inside 150 yards. Hornady 110gr V-MAX, Federal 120gr Fusion, and Barnes 110gr TAC-TX are purpose-designed expanding loads that expand reliably at .300 Blackout velocities. The cartridge performs best at ranges inside 200 yards — its ballistic coefficient drops off more rapidly than .308 or 6.5 Creedmoor at distance. For short-to-moderate range hunting from a compact platform, it's an excellent choice. Check state regulations — some states have minimum energy or caliber requirements for deer hunting that .300 Blackout may or may not meet depending on the load.

.300 Blackout vs. .223/5.56: When to Choose Which

.223/5.56 is lighter, less expensive, produces less recoil in a standard-pressure loading, and is available in a much wider range of factory loads. .300 Blackout delivers meaningfully more energy at short to moderate range, is the only AR-15 caliber with genuine subsonic suppressor capability, and requires only a barrel swap to run in a 5.56 lower. For most AR-15 users who don't own a suppressor and aren't hunting, .223/5.56 is the right choice. For suppressor hosts, hog hunters who want more energy in a compact platform, or anyone building a dedicated SBR, .300 Blackout justifies its cost premium. See our .223/5.56 ammo page for comparison.

AR-15 Compatibility: What Changes and What Doesn't

.300 Blackout uses a standard .223/5.56 bolt, carrier, lower receiver, and magazines — only the barrel changes. This makes converting an existing AR-15 to .300 Blackout a straightforward swap. The critical safety note: never chamber .300 Blackout in a .223/5.56 barrel. The .300 Blackout cartridge will chamber and fire in a .223 barrel but will destroy the barrel and can cause serious injury. In a household with both calibers, dedicated magazines labeled by caliber are essential to prevent mix-ups. Many .300 Blackout builders keep their .300 BLK magazines in a distinct color or with visible markings for this reason.

Pricing and Availability

.300 Blackout is priced higher than .223/5.56 but lower than most centerfire hunting calibers. Supersonic FMJ loads run approximately $0.60–$1.00 per round; subsonic loads run $1.00–$1.50 due to the heavier projectile. Federal, Hornady, Remington, and SIG all produce civilian-market .300 Blackout regularly. Buying subsonic loads in quantity when available is advisable — they sell out faster than supersonic loads and are less consistently stocked by retailers due to more limited overall demand.

Frequently Asked Questions: .300 Blackout Ammo

What is .300 Blackout best for?
The .300 Blackout is purpose-built for suppressed use in short-barreled AR-15s. Its primary advantages are: subsonic loads that are hearing-safe through a suppressor without the supersonic crack of other calibers, effective terminal performance from barrels as short as 9 inches (unlike 5.56, which needs 16 inches for full performance), and AR-15 magazine and lower receiver compatibility. For anyone building a suppressed short-barrel AR-15, .300 Blackout is the default choice.

What is the difference between supersonic and subsonic .300 Blackout?
Supersonic .300 Blackout (125-grain and lighter bullets at 2,100+ fps) behaves similarly to a mild 7.62x39mm — adequate terminal performance for hunting and defensive use, with a supersonic crack that a suppressor cannot eliminate. Subsonic .300 Blackout (220-grain and heavier bullets at 1,000–1,050 fps) is hearing-safe through a suppressor — the action cycling is the loudest sound. Subsonic loads are significantly less powerful and best suited for close-range suppressed use. Your intended application determines which you need.

Can a .300 Blackout rifle accidentally chamber .223 / 5.56?
Yes — this is a real safety hazard. A .300 Blackout cartridge will chamber in a 5.56 chamber but may cause a dangerous overpressure situation. A 5.56 round will not fully chamber in a .300 Blackout chamber but the risk of confusion when both calibers are present is real. Always label your magazines, keep calibers completely separate when loading, and confirm your magazine’s caliber before loading any .300 Blackout firearm. This is the most important safety consideration with the .300 Blackout.

What barrel length should I use for .300 Blackout?
.300 Blackout was designed around 9-inch barrels for suppressed SBR/pistol use — it achieves full powder burn in 9 inches, unlike 5.56 which loses significant velocity below 14.5 inches. For suppressed use, 9–10.5 inches is optimal. For unsuppressed use and hunting, 16 inches provides slightly higher velocity but the gains over shorter barrels are minimal compared to 5.56. The caliber genuinely shines in configurations 10.5 inches and under.