Basics About Exterior Ballistics
The term “Exterior Ballistics” can easily cause confusion and intimidation in shooters. However, it’s not as complex as it may sound.
Exterior Ballistics refers to the bullet’s flight between departing from the muzzle and hitting the target. However, there are numerous forces that can affect the bullet in its trajectory and, thus, affect your aim.
First, it’s important to remember that not every bullet is made the same. Some are sleek and made for speed, while others are square and strong and built for impact. As such, different bullets will react differently to their environment as they travel through the air.
Second, the firearm you’re using impacts the bullet’s trajectory as well. For instance, when shooting a handgun, the bullet’s travel time is fairly short. So the atmosphere and laws of physics have less of an opportunity to make an impact. However, if you’re shooting a high-power rifle, the atmosphere and physics can have a much more significant effect.
Knowing this, it’s important to consider the Ballistics Coefficient (or BC). This term describes the bullet’s ability to withstand the impact that things like atmospheric drag and wind drift can have.
Because a heavy amount of research has gone into studying Ballistics Coefficients, nearly all of the bullet boxes we have today come with a BC label on them.
The accuracy of a certain firearm is typically measured in the arc bridged by a minute of an angle (MOA). This is an angular measurement. One MOA equates to 1/60th of one degree on a circle. One MOA also equates to 1.047 inches at 100 yards (or 1 inch for simplicity purposes). Therefore, one MOA is 1 inch at 100 yards, 2 inches at 200 yards, and so on.
The spread of the ammo also plays a part in this. For instance, for a rifle that shoots MOA, a group of shots will be printed, measuring no larger than an inch of extreme spread at 100 yards. The further away the target is from the muzzle, the wider the arc is bridged by that angle.
For instance, if a hunter is facing shots within 400 yards, his/her MOA rifle will print a group that measures four inches at 400 yards.
Wind drift also plays an important factor when it comes to aim and accuracy. “Wind drift” essentially refers to the impact that a crosswind can have on a bullet’s trajectory. Although it is practically impossible to control the wind, it is also important to prepare for this as much as possible. After all, real-world situations often demand that a bullet hit its target no matter what.
Wind drift is tricky, because it can blow the bullet off course horizontally, as well as vertically. The measurement of wind drift is typically given in inches, but it can also be given in MOA. The conversion of these two is relatively simple. Regardless, MOS is an important measure when accurately adjusting telescopic sights.
Keep in mind this is a very brief overview of Exterior Ballistics. However, much more information can be found online.