Quick Answer
Temperature affects .338 Lapua ballistics by altering the air density and pressure, which in turn changes the bullet's velocity and trajectory. As temperature increases, the air density decreases, causing the bullet to travel faster and potentially impacting at a farther distance. Conversely, as temperature decreases, the air density increases, resulting in a slower bullet and a shorter impact distance.
Temperature Effects on Air Density
When temperature increases, the air expands and becomes less dense. This decrease in air density reduces the drag on the bullet, allowing it to travel faster. For example, a .338 Lapua bullet traveling at 2,900 ft/s at 70°F (21°C) will experience a 2.5% increase in velocity at 90°F (32°C) due to the reduced air resistance. Conversely, a decrease in temperature will increase the air density, resulting in a 2.5% decrease in velocity at 50°F (10°C).
Temperature Compensation for Long-Range Shooting
To compensate for temperature effects, long-range shooters use ballistic models and temperature correction charts. A commonly used temperature correction for the .338 Lapua is -2.5 ft/s/°F (4.4 ft/s/°C) above 70°F (21°C) and +2.5 ft/s/°F (4.4 ft/s/°C) below 70°F (21°C). This correction can be applied to the ballistic model to ensure accurate shooting at long ranges.
Practical Application of Temperature Compensation
In practice, temperature compensation is often applied in conjunction with other environmental factors such as humidity and barometric pressure. Shooters can use electronic ballistic calculators or temperature correction charts to determine the exact correction needed for their specific conditions. By taking into account the temperature effects on air density, shooters can improve their accuracy and extend their effective range.
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