.300 Blackout Ammo

What is .300 Blackout?

Advanced Armament Corporation and Remington Defense developed .300 AAC Blackout in 2010 because U.S. special operations needed a suppressed AR-15 that hit harder than 5.56 at close range. The 9mm MP5SD was the previous standard for suppressed work. AAC’s answer was to neck up a 5.56 case to accept a .30-caliber bullet — same bolt, same magazine, same lower. Swap the barrel and you’re running a completely different cartridge.

SOCOM adopted it. SAAMI standardized it in 2011. The commercial market ran with it.

One feature defines .300 BLK: a single rifle runs both supersonic (110gr at ~2,350 fps) and subsonic (220gr at ~1,010 fps) with nothing but an ammo swap. No other common AR-15 cartridge does this. That flexibility is the whole point.

Supersonic vs. subsonic

This is the choice you make every time you load magazines.

Supersonic (110–150gr, 2,000–2,400 fps from 16”):

Supersonic .300 BLK is roughly equivalent to 7.62x39 in energy. Better than 5.56 for terminal performance at close range — the bullet is heavier and wider. Past 200 yards it falls behind 5.56 because the lighter 5.56 bullets have better ballistic coefficients. Through a suppressor, supersonic rounds still make a sonic crack, but it’s noticeably quieter than unsuppressed.

Subsonic (190–220gr, 1,000–1,050 fps from any barrel length):

No sonic crack. Through a quality .30-caliber suppressor, subsonic .300 BLK drops to approximately 125–130 dB — near .22 LR levels. 150 yards is the practical limit before drop becomes unmanageable. For suppressed use, treat it as a 0–100 yard cartridge.

Bullet weight and what it means

The grain weight isn’t just a number — it changes what the cartridge does.

110–125 grain supersonic is the performance range. This is where .300 BLK earns its reputation for close-range terminal effectiveness. The 110gr V-MAX from Hornady Black is the community standard, expanding reliably at these velocities where cheaper bullets often don’t. The 125gr range is where most hunting and defensive loads live. At 2,100–2,350 fps, these bullets transfer energy fast and tumble aggressively in soft tissue.

147–150 grain is a transitional zone. These loads run supersonic from a 16” barrel but may go transonic or subsonic from a 9” barrel. Federal Fusion MSR 150gr is popular for deer inside 150 yards — bonded construction keeps the bullet together through shoulder bones. Avoid this weight range if your barrel is under 10”, as velocity becomes unpredictable.

190–220 grain subsonic is the reason the cartridge exists. At 1,000–1,050 fps, these are purpose-built for suppressor use. The 220gr Sierra MatchKing OTM is the accuracy standard at this weight; it doesn’t expand but it’s consistent and cycles reliably. The Hornady Sub-X 190gr is the right call if you need expansion at subsonic velocity — most conventional hollow points won’t open at 1,000 fps, and the Sub-X was specifically engineered to.

The bottom line on grain weight: Don’t run 147gr through a 9” SBR expecting consistent supersonic performance. Stick to 110–125gr supersonic or 190–220gr subsonic. The in-between range is more complicated than it looks.

Barrel length: it matters more here than in 5.56

Barrel length has a bigger effect on .300 BLK supersonic velocity than almost any common rifle cartridge. The powder is designed to burn fast in short barrels — by design for SBR and suppressor use — but you pay for it in velocity loss.

Subsonics don’t care about barrel length for velocity — they’re already slow. But gas port timing still matters for reliable cycling, which is why some very short barrels (under 8”) can have issues with subsonic loads.

Gas system cycling with subsonics

Most factory .300 BLK uppers cycle both supersonic and subsonic loads reliably. Problems show up in specific situations:

• No suppressor, subsonics: Some setups won’t cycle reliably without the added backpressure from a can. Test before depending on it.
• Adjustable gas block: Helps tune for both loads. Required if you’re having cycling issues.
• Heavy buffer: Many .300 BLK builds run a heavier buffer (H2 or H3) to improve subsonic cycling reliability.
• Very short barrels (under 8”): More problematic with subsonics. If you’re running a 7” pistol build, verify cycling with your specific setup.

The SIG Sauer MCX was specifically engineered for this — its short-stroke piston system cycles subsonics more reliably than a standard DI upper.

Should you even bother without a suppressor?

Honestly? Probably not.

Unsuppressed, supersonic .300 BLK is a mediocre cartridge. More expensive than 5.56, no steel-case ammo, shorter effective range, and similar energy to 7.62x39 — which you can shoot all day for $0.45/round. The only concrete advantage over 5.56 unsuppressed is that heavier .30-caliber bullets do more damage at CQB distances, and you can run it in your existing AR-15 lower.

If you’re planning to get a suppressor and want the quietest possible centerfire rifle on an AR-15 platform, .300 BLK is the right answer. The $200 NFA stamp and 8–12 month wait is one-time. Once you’re in, the subsonic experience is genuinely different from anything else you can do with an AR.

Safety: the one rule you can’t ignore

Never chamber a .300 BLK round in a 5.56 barrel.

The .300 BLK round physically fits in a 5.56 chamber and will headspace. When you pull the trigger, it destroys the barrel and can injure you or anyone nearby. This happens because shooters mix ammo between uppers — especially when running two uppers on one lower.

Prevent it: mark every .300 BLK magazine with colored tape, mag couplers, or dedicated aftermarket magazines. Do not mix .300 BLK and 5.56 mags in the same range bag. This isn’t a remote possibility — it happens regularly and the consequences are serious.

Common myths

“You need a suppressor to make .300 BLK worth it.” Mostly true for subsonic, not universally true. Supersonic .300 BLK in a short SBR gives you real terminal performance improvement over 5.56 at CQB distances without a can. The case for .300 BLK is weaker without a suppressor, but it’s not zero.

“You can use 5.56 dies to reload .300 BLK.” Partially true and dangerous if you don’t understand the difference. You can use a 5.56 sizing die trimmed to the right length, but .300 BLK requires correct case length trimming after sizing or you risk a dangerous chamber condition. Use dedicated .300 BLK dies.

“Subsonic .300 BLK won’t kill a deer.” Wrong at appropriate ranges. Inside 75 yards, a 220gr subsonic with a quality expanding bullet (Sub-X) generates more than enough energy for clean kills on deer-sized game. Shot placement matters more than velocity at that range. Check your state regs on suppressed hunting first.

“All .30-caliber suppressors are the same for .300 BLK.” The bore size matters, but so does the baffle design and flow rate. A suppressor rated for .30 caliber and designed for high-volume .308 fire may not cycle subsonics reliably on a shorter .300 BLK barrel. Short, lightweight .30-cal cans with active backpressure designs (like the SilencerCo Omega 300 or Dead Air Sandman-S) are better choices for a .300 BLK SBR than a full-length .308 can.

“Steel-case .300 BLK is coming.” It hasn’t materialized at any meaningful scale and there’s no sign it will. Lacquered steel-case ammo from Eastern European manufacturers hasn’t been adapted for .300 BLK in commercial quantities. Budget accordingly.

“Subsonics and supers use different magazines.” They don’t. Same STANAG magazines, same bolt, same lower. The only thing that changes is the ammo. This is also what makes the inadvertent mix-up with 5.56 possible — all three share visual similarities in the magazine.

Brand guide

Hornady Black 110gr V-MAX is the community standard for supersonic .300 BLK. The polymer-tipped V-MAX expands at .300 BLK velocities, which not all bullets do reliably. Consistent lot-to-lot performance. Around $0.75–0.95/rd.

Hornady Sub-X 190gr is the best subsonic load with an expanding bullet. The Sub-X tip initiates expansion at subsonic velocities, which most hollow points won’t do. Accurate, reliable cycling. Around $1.10–1.50/rd.

Barnes VOR-TX 110gr TAC-TX uses all-copper construction with 100% weight retention. Works in short barrels where cup-and-core bullets might not expand reliably. The choice for SBR home defense. Around $1.10–1.40/rd.

Federal Fusion MSR 150gr is a bonded hunting load designed for semi-auto platforms. Good penetration for deer inside 150 yards. Around $0.80–1.05/rd.

SIG Sauer 220gr OTM Subsonic cycles reliably in most platforms. OTM doesn’t expand but is accurate and consistent for subsonic range use. Around $0.90–1.20/rd.

Remington UMC 120gr OTM is the training standard. Cheaper than Hornady, reliable in most setups, not a hunting or defense load. Around $0.55–0.75/rd.

Fiocchi 125gr FMJ is budget training. Reliable. Around $0.55–0.70/rd.

.300 BLK vs 5.56 vs 7.62x39

Choose .300 BLK if you’re running a suppressor and want the best subsonic capability on an AR-15 platform, or if you need an SBR that hits harder than 5.56 at close range.

Choose 5.56 if you want longer range, cheaper ammo, or you’re not running a suppressor.

Choose 7.62x39 if you want AK-comparable energy without the AR-15 premium, and you’re fine with an AK platform.

Suppressor performance: what the numbers actually mean

A suppressor doesn’t eliminate sound — it reduces it. Unsuppressed .300 BLK supersonic runs around 165–168 dB, roughly equivalent to 5.56 from a short barrel. Through a quality .30-cal suppressor, supersonic .300 BLK drops to approximately 138–142 dB. That’s below the threshold most shooters use as a practical hearing-safe benchmark (140 dB), but it’s still loud enough to cause damage on sustained fire without hearing protection.

Subsonic is where the numbers get interesting. Subsonic .300 BLK through a quality suppressor runs 125–130 dB. That’s comparable to a .22 LR suppressed, and genuinely hearing-safe for limited shots. The mechanical noise of the action cycling is actually audible, which is not something you can say about most centerfire rifles. This is why special operations units used it — the sound signature is completely unlike a rifle.

The NFA process for a suppressor is: $200 tax stamp, Form 4 or Form 1 (if building), fingerprints, passport photos, CLEO notification, and a wait that currently runs 8–12 months for an approved dealer transfer. It’s one-time per suppressor. After that, the can is yours indefinitely.

Price guide (2025–2026)

No steel-case .300 BLK exists at any meaningful scale. Budget accordingly. If you’re running 500+ rounds per month, the cost difference between .300 BLK and 5.56 adds up fast — do the math before committing to the platform for high-volume practice.

Firearms chambered in .300 Blackout

Semi-automatic (AR-15 based):

• Any AR-15 lower with a .300 BLK upper — the most common configuration
• SIG Sauer MCX — purpose-built for .300 BLK, short-stroke piston, better subsonic cycling
• CMMG Banshee 300 — pistol-format, 8” barrel
• PSA 300 AAC series — budget-friendly AR builds
• Springfield Armory SAINT in .300 BLK

Bolt-action:

• Ruger American Ranch .300 BLK — suppressor-friendly, threaded barrel, subsonic-capable
• Mossberg Patriot in .300 BLK
• Christensen Arms Ridgeline in .300 BLK

The bolt-action options make sense for hunters who want suppressed subsonic capability without the SBR paperwork — a 16”+ bolt gun in .300 BLK is standard Title I, no NFA form required.

State purchase restrictions

California, New York, New Jersey, Illinois, Massachusetts, and Connecticut require permits, background checks, or other verification to purchase ammunition online. SendRounds filters retailers by shipping eligibility based on your location.