In previous blogs Shooting Range Industries have explored the advantage of the Ballistic Coefficient (BC) in BC-Part 1, and defined many key terms and concepts and other definitions as we can see that velocity plays a key role in long range precision engagements. Now we discuss how to calculate ballistic coefficient from velocity.
Long Range Shooting Wind Formula & How to Adjust
In practical situations, hunting and target shooting are the two factors that affect the bullets path are wind and shooting an incline. Wind acts over distance, the longer the bullet’s flight to the target the higher the wind effect. The slower the bullet translates to the target the more time the wind can act on bullet and deflect the bullet’s path. High ballistic coefficients offer shorter flight time, negating to a degree wind effects. Even so the Hornady A-Max match 155 grain 308 at 2700 fps at the muzzle will drift over 23 inches at 500 yards with a wind at a right angle to the bullets path with 10-mph wind. To illustrate the wind effect of over a distance, compare this to the same bullet at 250 yards with a deflection of about 5¼ inches. As the bullet progresses down range it is slowing, from 2700 fps to 2208 fps at 250 yards to 1771 fps at 500 yards, all conspiring to allow more time for the wind to batter the bullet in its flight. Wind angle to the bullets path will affect the outcome, a 45-degree wind will lower the drift to about 15 inches with the wind speed at 10 mph.
The other consideration is shooting up or downhill or at an incline.
Shooting Uphill & Downhill Aim Calculator
When shooting an incline, the vertical element is the dominate factor as the horizontal factor is diminished. The ballistic path of projectiles is calculated over a relatively long horizontal distance, with a moderate vertical influence. Incline shooting magnifies the vertical effect. Shooting up or down the bullet path will be lower. Intuitively this is counter to what one would expect shooting uphill. An example shooting a 15-degree incline, you would take the cosine of the angle and multiple it by range. Your range finder says 230 yards. The cosine of a 15-degree angle is .9659 times 230 equals 222.1629 yards, you will have to adjust your scope or hold 8 yards lower at 222 yards. The 222 yards is the TBR or True Ballistic Range. Some rangefinders can be set to calculate the TBR for you, it reads the incline angle and range and calculates the TBR. Experience indicates that the we are notoriously for estimating the incline high. We tend to estimate a 15 degree inclination higher to a much as 30 degrees. There are inclinometers that can attach to the gun/scope, range finders can include inclination and many a trail compass includes the means to determine up and down grades or slops.
This discussion has emphasized external ballistics. Along with incline estimation we tend to exaggerate range. To be fair most hunting shots are taken under 250 yards.
Point Blank Range
The next discussion is about point blank range. The target area of the typical game animal is described as a six to eight-inch diameter circle. The scope or sights are set to a range that allows the bullet to rise 4 inches above the bullet’s path, for an eight inch kill zone and drops to 4 inches below the path. There is no need to compensate for range as your bullet if aimed correctly will hit within the 8 inch kill zone. At the point-blank range, it will be dead on target. In hunting situations, you don’t have time to use a calculator or range finder, you will have to guesstimate the shot or use the SWAG method, scientific wild-ass guess. Point-blank aiming gives you more latitude for the successful shot. Doping the wind, calculating range and incline only comes with experience, demanding range time or informal plinking to hone your skills.
Custom Shooting Ranges for Military, Law Enforcement & Civilians
Stay tuned for the next blog in our series of ballistic coefficients. Contact Shooting Range Industries to learn more about hiring us to design and build your own a custom shooting range for firearms practice and training.