By Philip Massaro
“Dial up 21 MOA and give me one minute of wind left.”
So came the instructions from the spotter, as we engaged the 750-yard steel plate. As I broke the trigger and saw the hit, I reflected upon just how much science goes into hitting a distant target.
Think of a baseball’s path as it leaves the bat of a power-hitter, travels high into the sky and comes down into the upper deck, resulting in a home run. That curve, the “trajectory of its travel,” is what your bullet’s doing in its flight to its target. Formally, trajectory is defined as “the path followed by a projectile flying or an object moving under the action of given forces.” That path becomes more drastically curved as the distance from the rifle’s muzzle increases and the effects of gravity have time to rear their ugly head.
Ah, gravity. It tugs at a bullet launched from your rifle, just as it pulls your furniture to the floor and your feet to the ground. In order to strike our target, then, we need to elevate the muzzle of the rifle in order to compensate for the effects of gravity. This is what creates an arced trajectory.
Just how much the rifle’s muzzle needs to be elevated depends on several things. First is the shape and size of the bullet. (That shape in size collectively are known as “ballistic coefficient” or BC, but more about that in a minute.) The speed of the bullet, the distance to the target and the atmospheric conditions also play their parts. And the farther the target is from the muzzle, the more elevation will be required to compensate for gravity.
Addressing the speed issue, I refer back to the idea that all objects (generally) drop at the same rate. Accordingly, the faster a bullet can travel away from the muzzle, the more ground it can cover before dropping a prescribed distance. This is the reason many magnum cartridges are described as “flat-shooting.” They possess a higher velocity and, therefore, the bullet launched will cover more distance before dropping, and the resulting trajectory curve is flatter than that of a slower cartridge.
For the long-range shooter, adjustments in trajectory must be made to compensate for the given atmospheric conditions in order to hit the target. Atmospheric drag is the defining factor here. Thick air will slow a bullet faster than will thin air. The air at sea level tends to be denser than, say, the air at 5,000 feet, so even with all other components being equal, your rifle will not give the same trajectory curve with the same ammunition at both elevations.
I mentioned ballistic coefficient a couple of paragraphs back. This is a unitless number that assesses a bullet’s ability to overcome air resistance during its flight. Long, sleek bullets that slice through the atmosphere easily maintain velocity far downrange and travel further with less drop, while a short, flat-nosed bullet will slow down faster and require a more drastically curved trajectory in order to strike its target accurately.
The higher a bullet’s BC, the better it will resist atmospheric drag. If we compare two bullets of the same caliber and weight having different ballistic coefficients but sharing the same muzzle velocity, the bullet with the higher BC value will give a flatter trajectory.
Putting it Together — And, Yes, There’s an App for That
To understand how all this talk about trajectory relates to your time at the range, you need to also need to know how to make them work with your cartridge’s ballistics. Let’s look at what my spotter told me to do with that 750-yard target.
When he told me to “dial up 21 MOA,” he was talking about “minute of angle.” A minute of angle is a measure of arc equal to 1/60th of a degree, so, my spotter was telling me I would need to elevate my rifle’s muzzle — via a change in the position of the reticle in my scope — enough to make an angle of 21 minutes above the zero line to the target. This allowed for the amount the bullet would drop by the time it reached the target 750 yards away. Starting to see how this ties together?
The rifle I was using for that shoot was chambered for the popular 6.5 Creedmoor cartridge, and the scope on top had precise graduations that allowed me to precisely dial the necessary amount of elevation. Had I been using a cartridge with less velocity or with a bullet of lesser ballistic coefficient, the amount of elevation needed would have been more.
The data for my particular load, at that particular distance, was obtained from one of the many ballistic calculators available (I happened to be using the Hornady 4DOF program), which gave us information on trajectory, wind drift and many other factors useful to making the shot.
Today’s Distance Cartridges
The most popular target cartridges are popular for a couple reasons. They deliver a flat trajectory, usually using a bullet with a high BC, and they offer a recoil level that is tolerable to most shooters. Noteworthy magnum cartridges deliver higher-than-normal velocities and, thereby, flatter trajectories, but that comes with heavier recoil. (That can be mitigated with the use of a muzzle brake, but then there’s premature barrel wear.)
The .308 Winchester, 6.5 Creedmoor and 6 Creedmoor are examples of cartridges that represent a fantastic balance of long-range capability, flat trajectory and low recoil. The .300 Winchester Magnum, 6.5-284 Norma, 6.5 PRC and .338 Lapua offer heavier bullets, higher velocities or both, again with the price of increased recoil.
When it comes to distance target shooting, there is no cartridge that will shoot perfectly “flat.” All need muzzle elevation. Whether you use the elevation turret on your riflescope to make the adjustment or use a scope with a graduated reticle to measure the amount of elevation or holdover and achieve that trajectory is up to you, but you’ll need some means of precise measuring for successful distance shooting.
Just as an outfielder in baseball needs to elevate his throw in order to reach home plate, at distance the shooter must elevate the shot in order to hit the target. Knowing just how much to do that — and ultimately understanding the trajectory of your rifle — is paramount to hitting your target. Download a good ballistic calculator and take a look at how different bullets for your chosen cartridge perform at varying ranges. The more familiar you become with the trajectory of the cartridge and bullet combination you’ve chosen, the better a rifle shot you’ll become.
About the Author
Philip Massaro is a freelance writer whose passions include big game hunting and ballistics. He has appeared on numerous outdoor television programs and has authored books on both hunting and ballistics.
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