We started off this long range shooting series with an introduction to some important terminology. Now we’re ready to apply those terms. Let’s start with an introduction on a key external ballistics concept that directly relates to long range shooting: bullet trajectory.
From the moment it leaves the muzzle, a bullet starts to follow a descending parabolic trajectory. Which means that, as the bullet travels further, the rate at which it approaches the ground increases. This parabolic trajectory is caused by gravity and drag.
In fact, as soon as the bullet exits the barrel, it begins to fall toward the ground, attracted by gravity. The amount of drop caused by gravity is a function of bullet speed. Given a distance, the higher the bullet speed, the less is the time it is subjected to the effect of gravity and the less is its drop.
However, bullet speed is not constant; it starts to decrease as soon as the bullet exits the muzzle due to drag, the resistance that air offers to the bullet travel. As the speed decreases, the time the bullet is subjected to gravity increases, which, in turn, increases the amount of drop. This what gives the bullet its parabolic trajectory.
The amount of drag is determined by:
Bullet speed: Drag increases when the bullet speed, relative to the air, increases.
Ballistic coefficient: Bullets with higher BC are more efficient against drag.
Air density: The higher the air density, the higher is the drag. Density of the air depends essentially on:
- Altitude/Atmospheric pressure: the higher the atmospheric pressure, the higher the air density.
- Temperature: The lower the air temperature, the higher the air density.
- Relative humidity: The higher the relative humidity, the higher the air density. Anyway, humidity has negligible effects on bullet drop, at least under 1000yds.
Wind: If wind has a tail or head component, that is, if it does not blow perpendicular to the trajectory, it changes the speed of the air through which the bullet is flying. Therefore, the bullet speed relative to the air can change because of the wind changing the amount of drag on the bullet.
Wind can also affect the vertical component of the trajectory in a non-drag related manner. In fact, when a wind blows against a mountainside, a hillside, or a tall building, it generates a vertical component. A vertical wind can blow upward or downward, and the trajectory of a bullet that flies through it is deflected in that direction.
The Coriolis Effect is the effect of Coriolis force, that is, the force of the Earth’s rotation, on the bullet trajectory. Its effect is negligible, at least under about 1000yds, but we will examine this phenomenon in greater detail in the future.
Other factors must also be taken into account when dealing with the vertical component of the trajectory. These factors do not actually affect the trajectory, but are aiming or prospective related errors. They are:
Firing elevation/depression angle: When shooting at an angle, in other words, shooting uphill or downhill, with a certain amount of line of sight angle relative to the horizon, the bullet always hits higher than the aimed point. This happens whether you are shooting uphill or downhill. The wider the firing angle, the higher the point of impact. It has a considerable effect on bullet impact, so it must be taken into account, even at short ranges, if the angle is more than 30°.
Light: The amount of light, and the direction from which it came, changes the way we see the target through a telescopic sight because of optical effects and distortions. This leads to point of aim and, consequently, point of impact changes.
I will talk about uphill/downhill shooting and light’s effect more thoroughly in the future. But, in the next article, we’ll focus on what determines the horizontal component of the bullet trajectory.
AlessioBaldi hartcreek Physics dictates a trajectory which has assending and decending parts of the curve. Just because the shockwave is no longer pushing the bullet so many feet past the muzzle does not mean that the bullet will decend from that point.
AlessioBaldi hartcreek Physics dictates a trajectory which has assending and decending parts of the curve. Just because the shockwave is no longer pushing the bullet so many feet past the muzzle does not mean that the bullet will decend from that point.
hartcreek AlessioBaldi You are talking about the trajectory relative to the ground level, and you are right. The trajectory have an ascending and a descending part because to compensate for the drop we usually incline the barrel axis upward. If you’d shoot with the barrel parallel to the ground, you’d have only a descending trajectory. Relative to the barrel axis, the bullet always descend toward the ground. Drop indeed, is always negative.
What I want readers to understand now, is the trajectory relative to line of departure, since we make our compensation relative to that.
AlessioBaldi hartcreek From an observer that was directly above the target in line with a laser beam projected from the the center of the barrel, if the observer jumped off his perch above the target at the exact moment the rifle was fired, both would arrive at the target at the same instant and relative to the observer the bullet would have fallen all the way…Einstein
FateofDestinee hi dear i like to know from your experience about trajectory of bullet please help me
I’m sorry but unless things have changed a LOT in the world I’m not going for this statement.
“In fact, as soon as the bullet exits the barrel, it begins to fall toward the ground, attracted by gravity.
The amount of drop caused by gravity is a function of bullet speed.
Given a distance, the higher the bullet speed, the less is the time it
is subjected to the effect of gravity and the less is its drop.”
Speed has absolutely nothing to do with the drop of the bullet and a physics 101 student knows that.
It does have plenty to do with how far the bullet travels before it hits the ground but not the effect of gravity on the bullet given a 0 degree elevation. It starts to drop instantly when it leaves the barrel.
Hell even Myth Busters proved this. It’s basic physics. Frankly I am surprised.
Lost my interest at that statement.
Take Care.
A faster bullet will drop less over a given distance … that is what he said and is proven ballistic tables … you can play your semantics games if you want… your arrogance is annoying
The amount of drop caused by gravity is a function of time.
drop = f( time )
The amount of time to reach a target some distance away is a function of muzzle speed.
time to target = f( speed )
Therefore the amount of drop caused by gravity when reaching a target some distance away is a function of muzzle speed.
drop = f( time ) = f( f( speed) ) -> drop = f( speed )
The statement was not that the effect due to gravity is a function of speed (which would be incorrect), rather that the amount of time the bullet is subject to gravity is a function of speed.