Reliable 450 Bushmaster subsonic reloading data requires specialized reference tracking, as standard reloading manuals are primarily built for full-power supersonic factory loads. Published and lab-tested data typically covers heavy projectile weights ranging from 300 grains up to 410 grains. Data details starting and maximum subsonic powder charges, muzzle velocities kept strictly under the speed of sound (1,000 to 1,075 fps), chamber pressures running well below the SAAMI maximum limit of 38,500 PSI, cartridge overall length, and test barrel specifications. Because subsonic .450 Bushmaster loads utilize heavy bullets over reduced powder charges, minor component variations in brass case volume, small rifle primer selection, crimp tension, and suppressor backpressure can significantly impact velocity consistency and semi-automatic AR-15 cycling reliability.
450 Bushmaster Subsonic Reloading Data
| Bullet | Bullet Weight | Powder | Published Starting Load | Published Maximum Subsonic Load | Published Velocity | Barrel Length / Firearm | Source |
| Hornady XTP | 300 gr | Hodgdon Lil’Gun | 17.5 gr | 19.5 gr | 1,020 to 1,065 fps | 16″ / AR-15 Platform | Hodgdon / Lab Data |
| Hornady Sub-X | 395 gr | Hodgdon Lil’Gun | 16.0 gr | 19.0 gr | 1,030 to 1,066 fps | 16″ / Test Barrel | Hornady / Hodgdon |
| Cast Flat Nose | 400 gr | Accurate 1680 | 19.0 gr | 21.5 gr | 1,000 to 1,050 fps | 16″ / Gas or Bolt Gun | Western Powders |
| Hornady XTP | 300 gr | Accurate 1680 | 21.0 gr | 24.0 gr | 1,020 to 1,080 fps | 16″ / AR-15 Platform | Independent Testing |
| Cast Plain Base | 350 gr | IMR 4227 | 18.0 gr | 20.5 gr | 1,010 to 1,050 fps | 18″ / Ruger Ranch | Custom Handload Data |
Understanding The 450 Bushmaster Subsonic Data
Working up subsonic .450 Bushmaster loads requires a shift in mindset compared to standard reloading, since “maximum” in subsonic tables refers to velocity limits rather than pressure limits:
- Starting Load: The conservative minimum charge weight recommended to ensure clean propellant ignition and completely clear the heavy bullet from the bore.
- Maximum Subsonic Load: The ceiling charge where the bullet reaches the threshold of the speed of sound (~1,125 fps at sea level). Exceeding this value causes an unwanted sonic crack.Note: This is a velocity ceiling, not a pressure ceiling.
- Velocity: Quantified in feet per second at the muzzle. Ideal subsonic handloads target 1,000 to 1,075 fps to remain hearing-safe with a suppressor across changing atmospheric temperatures.
- AR-15 Gas Cycling: Because subsonic charges generate lower gas volume and pressure than factory supersonic loads, selecting the right powder (like Lil’Gun or Accurate 1680) is critical to cycle a semi-automatic AR-15 action, especially when a suppressor is attached.
.450 Bushmaster Subsonic Bullet Weight Options
Subsonic performance relies heavily on mass to transfer kinetic energy at lower impact speeds:
- 300 Grain (e.g., Hornady XTP): A popular mid-weight option that offers manageable recoil and stable flight, though standard hollow points may not expand reliably at true subsonic speeds (<1,100 fps).
- 395 to 410 Grain (e.g., Hornady Sub-X):Purpose-built heavy projectiles featuring specialized nose cavities engineered to expand reliably at low velocities, making them exceptional for suppressed hunting and home defense.
- 400+ Grain Cast Lead: Heavy, custom-cast flat-nose bullets that maximize momentum and punch deep tissue profiles at low velocities.
.450 Bushmaster Subsonic Powder Reloading Data
Selecting the correct powder involves matching fast-to-medium rifle propellants that maintain high case fill efficiency and consistent ignition under low pressure:
| Powder | Bullet | Bullet Weight | Published Starting Load | Published Maximum Subsonic Load | Published Velocity | Source |
| Hodgdon Lil’Gun | Hornady Sub-X | 395 gr | 16.0 gr | 19.0 gr | 1,030 to 1,066 fps | Hodgdon / Hornady |
| Accurate 1680 | Cast Flat Nose | 400 gr | 19.0 gr | 21.5 gr | 1,000 to 1,050 fps | Western Powders |
| Hodgdon Lil’Gun | Hornady XTP | 300 gr | 17.5 gr | 19.5 gr | 1,020 to 1,065 fps | Hodgdon |
| Accurate 1680 | Hornady XTP | 300 gr | 21.0 gr | 24.0 gr | 1,020 to 1,080 fps | Independent |
| IMR 4227 | Cast Plain Base | 350 gr | 18.0 gr | 20.5 gr | 1,010 to 1,050 fps | Custom Data |
Component And Assembly Best Practices
Because .450 Bushmaster uses straight-walled brass that headspaces off the case mouth, specific steps are required:
- Cartridge Overall Length (COL): Follow a maximum COL (typically around 2.245 to 2.260 inches) to ensure reliable feeding through standard AR-15 magazines and AR platform action gates.
- Primer Selection: Standard small rifle primers (SRI) are used. Many reloaders choose hard-cup military-spec primers to prevent slam-fires, though standard small rifle primers function smoothly.
- Crimp Requirements: A moderate taper crimp or light roll crimp into the bullet cannelure helps maintain uniform ignition timing and prevents bullet setback during aggressive semi-auto feeding.
Velocity Management And Suppressor Dynamics
Shooting subsonics through a suppressor requires strict attention to environmental factors. The speed of sound drops in cold weather (falling to roughly 1,080 fps at freezing temperatures). A load chronographed at 1,080 fps on a hot summer day may break the sound barrier and crack loudly during a cold winter hunt. Always aim for a target window of 1,020 to 1,050 fps.
Safety Warnings And Squib Risk
Subsonic reloading introduces unique hazards that require strict adherence to safety protocols:
- The Squib Load Hazard: Under-charging a large-capacity straight-walled case can result in a catastrophic “squib”—where the bullet lacks energy to exit the barrel. Firing a subsequent round into an obstructed bore will destroy your firearm and suppressor.
- Chronograph Verification: Always verify batch speeds over a chronograph to ensure safe subsonic performance.
- No Unverified Powders: Never guess or extrapolate charges for fast pistol powders without verified lab data, as secondary pressure spikes can occur in large rifle cases.
Best Sources For Subsonic Data
- Hodgdon Online Reloading Center: Features comprehensive, pressure-tested metrics covering propellants like Lil’Gun and H-110.
- Hornady Handbook of Cartridge Reloading: Provides factory data for heavy projectiles like the 395-grain Sub-X line.
- Western Powders Reloading Guide: Offers dedicated data listings centered around Accurate 1680 for big-bore straight-walled applications.
Common .450 Bushmaster Subsonic Questions
Where can I find .450 Bushmaster subsonic reloading data?
Reliable recipes can be accessed through the Hodgdon online data center, Hornady manuals, and Western Powders guides.
What are the best powders for .450 Bushmaster subsonics?
Hodgdon Lil’Gun and Accurate 1680 are widely regarded as the top propellants because they build sufficient port pressure to cycle semi-automatic AR-15 gas systems reliably.
What velocity should I target?
Aim for a muzzle velocity between 1,000 and 1,050 fps to ensure the round remains quietly below the speed of sound across different temperatures.
Will subsonic loads cycle an AR-15 without a suppressor?
Usually no. Subsonic loads generate lower operating gas volume; most semi-automatic AR-15s require the backpressure created by an attached suppressor to cycle properly.
Do standard bullets expand at subsonic speeds?
Most standard jacketed hollow points require velocities above 1,400 fps to open up. For ethical hunting or self-defense with subsonics, you must use specialized expanding options like the Hornady Sub-X.