Reliable .300 Blackout subsonic load data can be found directly through pressure-tested publisher resources like the Hodgdon Reloading Data Center, Hornady’s handbook, and Lyman manuals. Published load data normally includes the specific heavy .30-caliber bullet, cartridge overall length (COAL), powder type, starting charge, maximum charge, and expected muzzle velocities kept strictly below the speed of sound (typically under 1,050 to 1,100 fps). Common heavy bullet weights covered in these data sets range from 190 grains up to 220 or 240 grains, engineered specifically for suppressed AR-15 platforms. Major powder manufacturers publishing .300 Blackout data heavily favor fast-to-intermediate powders like Hodgdon CFE BLK, Accurate 1680, and Lil’Gun. Load data varies between sources due to differences in brass internal capacity (formed from standard 5.56 NATO cases), suppressor backpressure effects, and primer selection.
300 Blackout Subsonic Load Data
| Bullet | Bullet Weight | Powder | Published Starting Load | Published Maximum Load | Published Velocity | Barrel Length | Source |
| Hornady SUB-X | 190 grain | Hodgdon CFE BLK | 10.5 gr | 12.3 gr | 1,038 fps | 16″ | Hodgdon |
| Sierra HPBT | 220 grain | Accurate 1680 | 10.0 gr | 11.5 gr | 1,010 fps | 16″ | Western Powders |
| Hornady RN | 220 grain | Hodgdon CFE BLK | 9.8 gr | 11.2 gr | 1,005 fps | 16″ | Hodgdon |
| Nosler RDF / Custom | 220 grain | Hodgdon Lil’Gun | 8.5 gr | 10.0 gr | 985 fps | 16″ | Hodgdon |
| Berry’s Plated | 220 grain | Accurate 1680 | 9.5 gr | 11.0 gr | 1,020 fps | 16″ | Western Powders |
Understanding The .300 Blackout Subsonic Load Data
When examining a .300 Blackout subsonic load data chart, each data point provides critical safety markers established through laboratory pressure testing.
- Starting load: The minimum recommended powder charge formulated to ensure safe ignition, complete powder burn, and reliable semi-automatic cycling while keeping velocities safely under the speed of sound.
- Maximum published load: The highest powder charge tested under SAAMI pressure guidelines (operating at a max of 55,000 psi). Never exceed this figure.
- Velocity: Measured muzzle speed in feet per second (fps) kept tightly under ~1,080 fps to prevent a supersonic crack when using a suppressor.
- Pressure: The .300 Blackout is rated for up to 55,000 psi, though heavy subsonic loads often produce lower port pressures requiring optimized powder selection to cycle actions reliably.
- Bullet weight: Heavy projectiles (190gr to 220gr+) designed to maximize terminal momentum despite low velocities.
- Powder: Slow-to-medium rifle propellants like CFE BLK or Accurate 1680 that fill the case well and build sufficient gas volume for cycling heavy bullets.
- Barrel length: Standardized reference length (frequently 9 inches to 16 inches) which heavily influences gas port pressure and dwell time.
.300 Blackout Subsonic Bullet Weight Load Data
Because subsonic performance relies on mass rather than speed, projectile selection focuses heavily on heavy-grain profiles designed to expand at low impact velocities.
- 190 grain: Standardized by projectiles like the Hornady SUB-X. These offer a balance of expansion at lower speeds while maintaining cleaner powder-burning properties in shorter barrels.
- 200 grain: Popularized by cast, coated, or custom monolithic hunting bullets engineered to punch deep without fragmenting.
- 220 grain: The benchmark standard for .300 Blackout subsonic reloading data. Bullets like the Sierra MatchKing (HPBT) or Hornady Round Nose (RN) achieve maximum mass, maintaining momentum and quiet operation under 1,050 fps.
.300 Blackout Subsonic Powder Load Data
Selecting the correct propellant is vital because under-filling a large rifle case with light powder charges can cause extreme velocity spreads, inconsistent ignition, or dangerous secondary pressure spikes.
| Powder | Bullet | Bullet Weight | Published Starting Load | Published Maximum Load | Published Velocity | Source |
| Hodgdon CFE BLK | Hornady SUB-X | 190 gr | 10.5 gr | 12.3 gr | 1,038 fps | Hodgdon |
| Accurate 1680 | Sierra HPBT | 220 gr | 10.0 gr | 11.5 gr | 1,010 fps | Western Powders |
| Hodgdon CFE BLK | Hornady RN | 220 gr | 9.8 gr | 11.2 gr | 1,005 fps | Hodgdon |
| Hodgdon Lil’Gun | Nosler Custom | 220 gr | 8.5 gr | 10.0 gr | 985 fps | Hodgdon |
Never assume a powder charge designated for a supersonic 110-grain load can be used with a 220-grain subsonic bullet; doing so with heavy charges will cause catastrophic over-pressure.
.300 Blackout Subsonic Bullet And Powder Combinations
Safe handloading relies heavily on strict adherence to component matching:
- Case source and volume: Since .300 Blackout brass is frequently formed by cutting down and resizing standard 5.56 NATO or .223 Remington brass, wall thickness variations directly affect internal volume and seating depth.
- Cartridge Overall Length (COAL): Strict adherence to magazine limits (typically max 2.260 inches) is required to ensure smooth feeding in AR-15 platforms.
- Suppression and Backpressure: Subsonic data assumes the use of a suppressor, which increases backpressure and aids in reliable bolt cycling. Unsuppressed shooting with minimum loads may occasionally short-stroke.
.300 Blackout Subsonic Velocity From Published Data
| Bullet | Bullet Weight | Powder | Published Max Load | Muzzle Velocity | Barrel Length | Source |
| Hornady SUB-X | 190 gr | CFE BLK | 12.3 gr | 1,038 fps | 16″ | Hodgdon |
| Sierra HPBT | 220 gr | A-1680 | 11.5 gr | 1,010 fps | 16″ | Western Powders |
| Hornady RN | 220 gr | CFE BLK | 11.2 gr | 1,005 fps | 16″ | Hodgdon |
Always verify whether a recorded velocity comes from laboratory pressure testing or casual chronograph tracking. Subsonic velocities vary widely based on ambient temperature and elevation.
.300 Blackout Subsonic Load Data By Barrel Length
Barrel length significantly impacts .300 Blackout subsonic performance. While many laboratories test using 16-inch barrels, the cartridge is exceptionally popular in short-barreled rifles (SBRs) and pistols featuring 8-inch to 10.5-inch barrels. Shortening the barrel can drop muzzle velocities by 50 to 100 fps, meaning loads sitting right at 1,080 fps in a 16-inch barrel may drop safely into true subsonic territory, but borderlines must be monitored carefully via chronograph to avoid going supersonic.
.300 Blackout Subsonic Energy And Ballistics
Based on manufacturer-published data for a 220-grain bullet leaving the muzzle at 1,010 fps:
- Muzzle: 1,010 fps / 498 ft-lbs energy
- 50-yard: ~975 fps / 464 ft-lbs energy
- 100-yard: ~945 fps / 436 ft-lbs energy
Subsonic ballistics feature a pronounced arc due to the low velocity, requiring careful drop compensation past 100 yards while delivering quiet, heavy-mass impact energy.
.300 Blackout Subsonic Load Data For Hunting
Subsonic .300 Blackout loads using specialized expanding projectiles (such as the Hornady SUB-X or solid copper expanding monolithics) are widely used for short-range pest control, wild hogs, and deer inside 75 to 100 yards. Traditional non-expanding target bullets (like standard FMJs or match HPBTs) at subsonic speeds will pencil through game without creating adequate wounding channels, making bullet selection critical for ethical hunting.
Manufacturer Data vs Independent Testing
- Manufacturer data: Formulated via piezoelectric pressure barrels by industry leaders (Hodgdon, Hornady, Western Powders). This is the definitive safety standard.
- Independent testing & user reports: Sourced from hobbyist forums. These should be treated carefully, especially when tuning gas blocks or custom buffer weights for suppressed fire.
.300 Blackout Subsonic Pressure And Safety
Operating at a maximum average pressure of 55,000 psi, the .300 Blackout requires strict discipline. Because subsonic loads utilize smaller powder charges inside a large rifle case, double-charging a case is a severe hazard if proper bench practices are not enforced. Always verify powder levels visually before seating bullets.
Best Sources For .300 Blackout Subsonic Load Data
- Hodgdon Reloading Data Center: The premier online repository featuring extensive pressure-tested data for CFE BLK and Lil’Gun.
- Hornady Handbook of Cartridge Reloading: Offers specialized data optimized for SUB-X and InterLock projectiles.
- Western Powders Reloading Guide: Essential reference data for Accurate 1680.
Common .300 Blackout Subsonic Load Data Questions
Where can I find .300 Blackout subsonic load data?
Directly from the Hodgdon online data center, Hornady manuals, and Western Powders guides.
What powders work best for subsonic loads?
Hodgdon CFE BLK and Accurate 1680 are widely regarded as the industry standards for cycling subsonic loads reliably.
What is the ideal velocity for subsonic data?
Velocities should stay comfortably below the speed of sound, typically between 980 fps and 1,050 fps, to avoid a sonic crack.
Can standard rifle primers be used?
Yes, standard Small Rifle primers are specified in nearly all published .300 Blackout reloading manuals.
Final Verdict
Reloaders producing .300 Blackout subsonic ammunition should exclusively utilize verified, pressure-tested data from established sources like Hodgdon, Hornady, and Western Powders. Paying close attention to bullet expansion design, powder volume filling, and muzzle velocity limits ensures both safe operating pressures and reliable, quiet performance through suppressed firearms.