The .300 AAC Blackout occupies a unique corner of the cartridge world: it runs in a standard AR-15 lower with only a barrel swap, it cycles both subsonic and supersonic loads from the same magazine, and when paired with a suppressor, it produces one of the quietest centerfire hunting experiences available. That flexibility makes it genuinely useful — and genuinely interesting to reload.

The catch is that reloading the Blackout requires more discipline than most cartridges. The case is short, powder volumes are small, and the consequences of a compressed or overpressure load in a suppressed firearm are magnified. Do this right, and you'll have a versatile, accurate, economical round. Cut corners, and you'll regret it.

Brass Selection and Preparation

The .300 Blackout is formed from 5.56 NATO or .223 Remington brass trimmed to 1.368 inches and reamed to accept the larger .30-caliber bullet. Dedicated Blackout brass (Starline, Peterson, Hornady, Lapua) is available and worth buying if you're starting fresh. It eliminates the trimming step and ensures consistent case length.

Case Prep Steps

  • Full-length resize: Essential for semi-auto reliability. Use a carbide die to reduce friction.
  • Trim to length: Max case length is 1.368 inches. Trim to 1.358 inches for consistency. Cases that are too long can jam into the leade and create dangerous pressure spikes.
  • Deburr and chamfer: The short neck requires careful chamfering to seat heavy bullets without shaving the jacket.
  • Primer pocket uniforming: Less critical than in precision rifle cartridges, but worth doing on match loads.

Military 5.56 brass used for conversion has crimped primer pockets — you'll need to swage or ream them before repriming. Failure to do so will result in high resistance and inconsistent ignition.

Primer Selection

Use small rifle primers for the Blackout — not small pistol primers, which some beginners assume due to the round's pistol-like powder volumes. Standard small rifle primers work well for most loads. For subsonic loads with slower powders, a magnum small rifle primer can improve consistency in cold weather, but is not required for most applications.

  • CCI 400: Reliable all-around choice, widely available
  • Federal 205M: Match-grade consistency for bench use
  • CCI 450 (Magnum): Optional for cold-weather subsonic reliability

Powder Selection

Powder choice in the Blackout depends entirely on what you're loading: supersonic hunting/target loads or subsonic suppressor loads. These two applications require completely different powders, and the distinction is not subtle.

Supersonic Loads (100–135 grain bullets)

Supersonic Blackout loads function like a short, efficient .30-caliber round optimized for short barrels (9–16 inches). You need powders that burn fast enough to fully combust in a short barrel:

  • Hodgdon CFE BLK: Purpose-designed for Blackout. Excellent velocity, meters well, good copper fouling reduction. Best all-around supersonic choice.
  • Hodgdon H110: Dense, consistent, great for 110–125 grain bullets. Requires careful charge weight — do not reduce below minimum loads.
  • Lil' Gun: Excellent in short barrels with 110–125 grain bullets. High velocity, good consistency.
  • IMR 4227: Classic pistol/Blackout powder, reliable and available.

Subsonic Loads (190–220 grain bullets)

Subsonic loads require slow-burning, high-density powders that fill the case adequately and maintain consistent ignition without building enough pressure to push bullets past ~1,000 fps. Too fast a powder = supersonic velocity. Too slow = inconsistent ignition and potential squib loads:

  • Hodgdon CFE BLK: Also works well for subsonic — versatility is a selling point.
  • Alliant 1680: The most popular subsonic choice among serious Blackout reloaders. Consistent, fills the case well, excellent ignition with heavy bullets.
  • IMR 4227: Works for both supersonic and light subsonic loads.
  • Accurate 1680: Same burn rate as Alliant 1680, often more available. Excellent choice.

Starting Load Data

Always begin at the published minimum load and work up in 0.3-grain increments. The following data is for reference only — consult a current reloading manual for verified data.

Supersonic Reference Loads

  • 110 gr V-MAX + CFE BLK: Start 18.0 gr / Max ~20.5 gr | Vel: ~2,250–2,400 fps (16" barrel)
  • 125 gr Nosler Ballistic Tip + H110: Start 18.0 gr / Max ~19.5 gr | Vel: ~2,100–2,200 fps
  • 130 gr Maker REX + Lil' Gun: Start 16.5 gr / Max ~18.5 gr | Vel: ~2,050–2,150 fps

Subsonic Reference Loads

  • 220 gr SMK (Sierra MatchKing) + 1680: Start 9.0 gr / Max ~10.5 gr | Vel: ~980–1,010 fps
  • 208 gr Hornady A-MAX + CFE BLK: Start 9.5 gr / Max ~11.0 gr | Vel: ~960–1,005 fps

Critical note on subsonics: Never download below the published minimum. Insufficient powder charges can cause squib loads in semi-auto actions — a catastrophic failure risk, especially in suppressed firearms.

Bullet Selection for Hunting

For deer-sized game with supersonic loads, the 110 gr Hornady V-MAX, 125 gr Nosler Ballistic Tip, and 130 gr Maker REX are all proven performers. For subsonic hunting (usually within 100 yards), heavy expanding bullets like the 220 gr Sierra MatchKing are not ideal — they're match bullets that don't expand reliably. Look instead at the 200 gr Hornady Sub-X, purpose-designed for subsonic expansion, or the 190 gr Sierra GameChanger for subsonic performance on deer.

Accuracy Expectations

A quality 16-inch Blackout barrel should group supersonic handloads under 1.5 MOA consistently, with top loads approaching sub-MOA. Subsonic loads in a quality barrel will typically group 1–2 MOA at 100 yards — which is perfectly adequate for their intended 150-yard-and-under hunting range. If you're seeing larger groups, look first at brass consistency and seating depth before changing powder.

Suppressor Considerations

Running a suppressor creates back-pressure that can affect cycling reliability. You may need to adjust your AR's gas system — a fully adjustable gas block (Superlative Arms, SLR Rifleworks) lets you tune for both suppressed and unsuppressed operation. Start with a standard setting and reduce gas if you experience bolt-over-base failures or excessive bolt velocity.

The .300 Blackout rewards careful reloaders with genuine versatility. Few cartridges let you switch from a quiet 960 fps subsonic to a 2,350 fps deer load without touching anything but the magazine. That flexibility, backed by well-developed handloads, makes the Blackout one of the most interesting rounds in the modern hunter's arsenal.