The .308 Winchester, a stalwart of the shooting world, finds new life in the subsonic realm. Subsonic ammunition, traveling slower than the speed of sound (approximately 1125 feet per second), offers distinct advantages: reduced noise, increased accuracy at longer ranges due to less bullet drop and wind drift, and suitability for suppressed firearms. This guide delves into the crucial aspects of 308 subsonic load data, covering everything from choosing the right components to achieving optimal performance.
Understanding Subsonic Ballistics
Before diving into load data, understanding the unique ballistic characteristics of subsonic .308 ammo is essential. The lower velocity significantly impacts bullet trajectory, energy retention, and overall effectiveness.
- Reduced Recoil: The lower velocity translates directly to reduced recoil, making subsonic .308 easier to shoot for beginners and more comfortable for extended shooting sessions.
- Increased Accuracy Potential (at certain ranges): While energy is lower, the reduced velocity can lead to greater accuracy at ranges where higher-velocity rounds are significantly impacted by wind and bullet drop.
- Sound Suppression: The primary advantage. Subsonic rounds generate significantly less noise, making them ideal for hunting in noise-sensitive areas or tactical situations where sound signature is critical.
- Challenges: Subsonic ammo often exhibits less stopping power than supersonic counterparts, necessitating careful shot placement. Also, achieving stable flight at subsonic velocities can be tricky and requires specific bullet and powder combinations.
Choosing the Right Components for Your 308 Subsonic Loads
Selecting the correct components is crucial for safe and effective subsonic .308 loads. The wrong combination can lead to inconsistent performance, pressure issues, or even dangerous malfunctions.
Bullets: The Foundation of Subsonic Performance
Heavy, well-designed bullets are key to success. These bullets are more stable at lower velocities, maintaining accuracy and reducing the chances of keyholing (the bullet tumbling and striking the target sideways). Look for bullets specifically designed for subsonic use, often with a heavier profile and boat-tail design.
- Weight: Consider bullets weighing 150 grains or heavier. Heavier bullets are less affected by air resistance at lower velocities.
- Construction: Solid copper or jacketed lead bullets are common choices. Choose a bullet construction appropriate for your intended purpose.
- Sectional Density: A higher sectional density (SD) means better penetration and resistance to wind drift.
Powders: The Driving Force Behind Subsonic Velocity
Powder selection is equally critical. Subsonic loads require powders that burn efficiently at lower pressures to produce sufficient velocity without exceeding safe pressure limits.
- Slow-Burning Powders: Powders with a slower burn rate, such as Accurate Arms #9, Hodgdon Titegroup, or others specifically recommended for subsonic loads, are generally preferred. These powders are better suited to generating consistent, accurate pressure curves within the lower velocity range.
- Powder Measurement: Precise powder measurement is paramount with subsonic loads. Use a scale accurate to 0.1 grain to ensure consistent results and avoid dangerous over-pressure.
Cases and Primers: The Building Blocks
While less influential than bullets and powders, proper cases and primers contribute to overall performance and safety.
- Cases: Use new or once-fired cases in good condition. Avoid damaged cases that could lead to pressure issues.
- Primers: Use standard small rifle primers. Experimentation may be needed to find the primer that provides consistent ignition.
Sample 308 Subsonic Load Data
Disclaimer: This load data is for informational purposes only. Always consult reloading manuals from reputable sources, such as those published by powder manufacturers, before attempting any reloading. Never exceed maximum recommended pressures. Improper reloading can lead to serious injury or death. This data is provided as a starting point and may not work optimally in all firearms.
| Bullet Weight (grains) | Powder (Type) | Powder Charge (grains) | COL (inches) | Velocity (fps) (approximate) | Notes |
|---|---|---|---|---|---|
| 150 | Accurate Arms #9 | 12.0 | 2.800 | 1050 | This is just a starting point. Adjust accordingly based on your firearm. |
| 168 | Hodgdon Titegroup | 9.5 | 2.850 | 1000 | Start low and work your way up, monitoring pressure signs carefully. |
| 200 | IMR 4227 | 13.5 | 2.900 | 950 | Consult the manual for appropriate case length. |
Note: COL (Cartridge Overall Length) needs to be adjusted based on your chosen bullet and seating depth to avoid feeding issues in your firearm. Always check for sufficient case clearance in your chamber.
Safety Precautions: Reloading Subsonic .308 Ammunition
Reloading ammunition, especially subsonic loads, requires careful attention to safety. Following these guidelines is crucial:
- Consult Loading Manuals: Always refer to and follow manufacturer load data precisely.
- Proper Equipment: Use only high-quality reloading equipment properly maintained and calibrated.
- Wear Safety Gear: Always wear safety glasses and ear protection when reloading.
- Accurate Measurements: Use a powder scale for precise powder measurements.
- Careful Inspection: Inspect each round carefully before loading and firing for any defects or irregularities.
- Start Low and Work Up: Begin at the low end of the load data range and gradually increase powder charge, closely monitoring pressure signs and observing any changes in velocity, accuracy and functionality.
- Pressure Signs: Be aware of pressure signs: flattened primers, excessive case bulging or expansion, or unusually high felt recoil.
Conclusion
Loading subsonic .308 ammunition offers a unique blend of stealth, accuracy, and reduced recoil. While demanding precision and a thorough understanding of reloading principles, the rewards—quieter shooting and potentially enhanced accuracy—make it a worthwhile pursuit for experienced reloaders. Remember, safety is paramount. Always prioritize safety, consult reliable sources, and start low and go slow to avoid incidents.