What are the factors that affect accuracy and precision?
-By Sanjay Soni, MD of Hughes Precision Manufacturing
Several factors come into play when you pull the trigger, such as temperature, altitude (barometric pressure) and wind speed. The Atmospheric temperature, the gun barrel, and the ammunition all play a small but significant part in the accuracy of your shot.
Let’s take a look.
Temperature of the Gun Barrel
When a barrel heats up, the gun becomes less accurate.
Both the friction of the bullet and the exploding charge propelling it heats up the gun barrel. The internal barrel will expand slightly, allowing some of the exploding charge to leak past the bullet, reducing speed and momentum and affecting the accuracy of the shot.
Temperature of the Ammunition
When snipers go for long (~1 mile) shots, they take out the magazine and leave it in the sun, allowing the ammo to warm up. They will then load a single bullet at a time since a warm bullet is likely to be more accurate.
Most military small-arms propellants are relatively sensitive to temperature. Warming ammunition in the sun or under a coat has nothing to do with expanding the diameter of the projectile, but is rather about wringing the last bit of muzzle velocity out of the round's propellant.
Atmospheric Temperature
Temperature alters a bullet’s trajectory in two ways. The first change takes place in the chamber and cartridge itself. This is known as the internal temperature. The second is the air temperature outside, known as the external temperature.
As the temperatures rise, muzzle velocity increases while air density gets thinner, reducing the drag on the bullet. If the ammo is not shaded from the sun, the warm propellant will increase chamber pressure, making the bullet fly faster. This higher velocity causes a flatter trajectory and results in the bullet striking the target slightly higher than a slower moving bullet.
Combined with the thinner air density, even the best marksman will find it difficult to strike the target dead center unless sight adjustments are made.
High temperatures also cause mirages. A mirage is a good indicator of wind speed and direction. It can also cause image distortion, with the target appearing to be moving in a wavy fashion. In that case, you need to reduce scope magnification for a clearer image.
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