External Ballistics

GRAVITY

Once you fire a bullet, gravity immediately begins to pull a bullet back towards earth. This is a reliable constant (gravitational acceleration) of 9.8m/s/s or 32ft/s/s.

TERMINAL BALLISTICS

Terminal ballistics is the study of how the bullet effects the target. The main thing is to hit the vitals. Also of tremendous importance is how the bullet damages tissue in game animals. The permanent wound cavity is essentially what tissue gets destroyed by the bullet as well as any bone etc… an expanding bullet creates a more significant crush cavity than full metal jackets or the like. Monolitic or stout bonded bullets are a blend. This is unsettled science, but at RBO we have thousands of experiences and we strongly lean towards fragmenting expanding bullet.

AIR DENSITY

This is the measure of air pressure, temperature and the humidity of the air that the bullet must travel through. Air pressure is referenced as Barometric Pressure or Station Pressure. We will be referencing station pressure, which is uncorrected air pressure. Barometric Pressure is corrected for sea level and the standard is 29.92 at 59 degrees. We will be referencing inHg as our units of measure but their are others like psi etc…If we use station pressure the altitude is not required because we use the actual uncorrected pressure so we know the precise value of the air resistance. If we use Barometric pressure then altitude must be included in our equation. Tools to measure Station Pressure include, Kestral weather stations, watches such as ABC sensor watches like Suunto or Casio’s, and many of today’s rangefinders incorporate weather stations onboard with ballistic programs.

BALLISTIC COEFFICIENT - (BC)

This is a numerical value associated with the ability of a bullet to withstand air density. The higher the number the better. Their are different standards used to measure BC’s but we usually reference G1 and G7.

Muzzle Velocity

How fast the bullet is traveling. Faster is good but minimal variation is more important. The faster the bullet is traveling the less time the air density has to effect it. The more consistent the bullet is traveling the lower the dispersion of the bullet fan will be. We strive for a Standard Deviation of 10 FPS or lower.

Weather

Temperature- higher temps lead to lighter air. Humidity- Higher humidity leads to lighter air. Wind- The most difficult part of external ballistics. Wind upon the bullet pushes the bullet and must be accounted for. The wind must be accounted for all the way from the muzzle to the target. Weather stations can help at the muzzle, but other indicators like mirage, and reading vegetation along the bullets path will also be incorporated to come up with a solution. One of the main reasons that we try to use bullets with higher BC numbers is to lessen the effects of wind on our bullet.