Consider for a moment that earth’s gravity is constant. Though fluctuations exist we will be referencing the equatorial sea level average of 32.17 feet per second per second. Once a bullet leaves the barrel two forces begin to act to diminish range and velocity. Gravity will pull the bullet towards the earth’s surface (gravity acts center to center between two objects, the bullet and the earth in this case) at about 32.17 feet per second, every second. The two factors act to retard forward motion, or drag caused by the air, the other is shock wave generation. Bullets that move at higher velocity than about 1050-1100 feet per second are supersonic. The bullet creates a shock wave at the point. This mini-sonic boom is the crack heard as the bullet passes a target, and why supersonic bullets cannot be silenced. But this shock wave is not directional. You know you’re being shot at, and missed but you cannot tell from what direction if the shooter is using a suppressor. Generating this shock wave requires a relatively high amount of energy. This ‘bow’ wave is responsible for retarding forward velocity more than the atmospheric drag.
Does a Bullet Rise When it Leaves the Barrel?
From shooter to target the bullet is dropping after it noses over at apogee, the highest point of the bullet arc. We fire upwards at an angle to compensate for bullet drop, this arc stretches out from the muzzle forming an upward angle of departure. If our gun is sighted in at a hundred yard there will be zero drop, at the 100-yard mark. Let us do some ballistic comparisons. Keeping everything standard we will compare the bullet drop from ‘0’ at a hundred yards to 250 yards, about the maximum range of most successful hunting.
Velocity in Shooting Bullets
We are going to use Hornady’s online ballistic computer. To pick a standard we will use the 7.62 x 51mm NATO round, the civilian version is the 308 Winchester and the bullet is the Hornady 168 grain Boat Tail Hollow Point a match bullet designed to be ‘slippery’ through the air. This bullet in the data listed can reach 2700 feet per second velocity from their test firearm a model 70 Winchester, bolt action with a 22-inch barrel. At the high end we’re going to send the same bullet down range from a Remington 700 bolt action in 300 Winchester Magnum with a 25-inch long barrel. This same bullet leaps from the muzzle at 3200 feet per second in this firearm and is also sighted for ‘0’ drop at 100 yards. The 308 Winchester from a 0” inch drop at one hundred yards the bullet is a 8.5” lower at 250 yards, traveling a total between the two ranges of 150 yards. With a muzzle velocity of 2700 fps, the bullet is chugging along at 2503 fps at 100 yards and dropping to 2223 fps at 250 yards. Over this distance the bullet averages 2383 fps. The flight time is 755 milliseconds. The mighty 300 Winchester Mag manages 3200 fps at the muzzle and is still zipping along at 2979 fps with ‘0’ drop and is a speedy 2669 fps, just below the 308’s muzzle velocity. The average velocity is 2824 fps, with only a 5.3” drop over the 150 yards for an itinerary of about 638 milliseconds. This illustrates the factor velocity plays and why higher velocities are flatter.
In a future discussion, we will see what the ballistic coefficient does for us.