Given that there is an infinite number of bullet types, weights, and shapes, doing all the math for each would be an impossible task. The goal was to be able to predict how far projectiles would travel, the arc of flight, and at what velocity they would impact targets. Back in the day, guys with lots of time on their hands fired boatloads of projectiles to figure out how they behaved in flight. Simply put, ballistic coefficient is a fudge factor. Ballistic Coefficient numbers are fudge factors that adjust for how each projectile performs relative to the standard model. The original G1 ballistic bullet models were based on a standard bullet like this. A bullet with a high ballistic coefficient is slippery and less subject to drag ( slowing down) as it continues on its merry way. What is Ballistic Coefficient?īallistic coefficient (BC) is a mathematical representation of how efficiently a bullet flies through the air. Oh, and because our two example bullets above have the same weight and diameter, hence the same frontal surface area, the sectional density numbers are the same. Bullets with low sectional density are short and fat. To grossly abuse math and physics, bullets with high sectional density are long and skinny. Technically, it’s the ratio of the weight to the surface area, but it’s easier to think in terms of diameter as that’s how bullets are measured. Simply put, sectional density is the ratio of weight to the diameter of the bullet. The nail flying point forward has a very highsectional density because it’s long and skinny. It’s long and narrow, so the surface area pointing into the wind is very small. A quarter flying this way makes a lousy bullet, right? So, in this case, the quarter has a very lowsectional density because its mass is divided by a large number that represents its surface area. From front to back along the flight path, the quarter is only 0.069 inches “long” when it’s flying face first because that’s the thickness of a quarter. We’ve got a big wide object pummeling its way through the air towards the target. Imagine launching a quarter at a target, but we somehow get it to fly face first, so the “top” flat side with George’s head is leading the way. That’s way too complicated, so let’s use an illustration. Sectional Density is a measurement that reflects the ratio of something’s mass to its cross-sectional area. As Sectional Densityis a key input to Ballistic Coefficient, we’ll look at that first. Two measurements that help define the downrange performance of a bullet are ballistic coefficient and sectional density. So why the significant differences even though bullets were of the same diameter, weight, and velocity? That boils down to more complex factors like shape, length, and weight distribution. Rest assured, there will be performance differences between every two bullet designs of the same weight and different shape, just not as dramatic. As a shorter-range hunting bullet, it’s going to show the impacts of differences in ballistic coefficient more dramatically. OK, so with the Sierra flat point Pro-Hunter, I picked an unusual bullet to illustrate a long-range shooting ballistic concept, but that’s OK. 308, 150-grain bullet, but it has a much lower ballistic coefficient. In the world of ballistic coefficients, a bigger number means that a bullet flies more efficiently. The Matchking has a coefficient of 0.417. The flat point Pro-Hunter has a ballistic coefficient of 0.185. These two bullets, while of the same weight, have different ballistic coefficients. After running the trajectory numbers based on atmospheric conditions here where I live in South Carolina, we get the following results.
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