Have you ever used a ballistic application and seen “BC”, but not known what it meant? It means “Ballistic Coefficient”, and it’s important. When you incorporate science and math into long-range shooting, you substantially increase the likelihood of success. Over 200 years ago, ballisticians began trying to understand drag and how to calculate the effect of drag on a projectile’s trajectory. Today, the ballistic coefficient of a bullet is used to predict what ballisticians set out to do long ago.
Term: Ballistic Coefficient
Also Known As: BC
Application(s) of use: Rifle shooting (i.e. long range and hunting)
Definition: According to Hornady, “A ballistic coefficient is the measure of a bullet’s relative ability to overcome air resistance.” Merriam-Webster defines ballistic as: “of or relating to ballistics or to a body in motion according to the laws of ballistics.” And, coefficient is defined as: “a number that is used to measure some property or characteristic of a substance“.
Why it Matters: An accurate BC will help you hit your target when using ballistic engines or applications. BC is relative to a standard projectile and is used to fill the formula for ballistic calculators. If you take nothing else from this language lesson, just know that you input the BC into your ballistic software/engine/application so it can predict where your projectile will hit down range.
Into the Weeds: Below is a little more in depth explanation than what the average shooter needs to know.
BC is a number assigned to a projectile to give a measurable value as to how efficiently it penetrates the air. This lets you know how quickly it’ll drop and how much it’ll be moved by wind. Here’s the catch: the BC of a bullet is relative to the environmental conditions it was shot in during testing. So, the manufacturer’s listed BC is true to both the conditions and distance the projectile was tested. Distance matters because it relates to the velocity of the bullet and its amount of drag.
To determine the BC of a bullet, having a constant in the equation allows for more precise calculations. The constant for the BC equation is the standard projectile profile which the other projectile (your bullet) can be compared to; the standard has a value of 1.0. When trying to anticipate how a bullet will react once it leaves the barrel, it’s best to compare it to a bullet profile that is most similar.
There are a handful of standard projectile models; the most frequently and longest used is the G1 standard. Since many manufacturers have been using the G1 standard, a bit of math is involved when trying to figure out how a more aerodynamic bullet will perform (like modern rifle projectiles we use today).
Because of the math involved, the BC listed on a box of modern rifle ammo will have a higher number if the G1 standard is used. Do not let this fool you into thinking it’s a better bullet just because the number is high. Without going down a rabbit hole, I’ll tell you that the G7 standard profile will get you closer to knowing how your projectile will react downrange.
When Bryan Sikes explains BC, he compares it to a parachute; “I say, imagine the lower the BC, the bigger the parachute is on the back of a projectile. This parachute represents the inefficiency of lower BC projectiles by way of less retained velocity which directly correlates to time of flight. I believe this is the key to everything as far as external ballistics are concerned.”
In Summary, the ballistic coefficient is a number assigned to a projectile to provide a unit of measure for how the bullet will react when shot due to it’s ability to overcome air resistance. For the most accurate output, select a ballistic program that allows for a G7 profile input. There are several variables that go into being able to hit a target at long distances. Factors like: you, the rifle, the ammo, and the environment all directly affect that round as it travels to the target. Having an accurate BC is just a tool to help you mitigate some of the variables of long range shooting.
Go get your learn on at Applied Ballistics. Applied Ballistics is the brainchild of Ballistician, Bryan Litz. His books have the best information available to help you hit targets waaay downrange and actually assist in understanding how to duplicate that hit. Follow Applied Ballistics on Facebook here.
Question for the crowd: When you’ve used a ballistic calculator, do you adjust density altitude, velocity, or ballistic coefficient to get your approximate point of impact at long range?
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