What causes bullet drop?

P

Pond James Pond

New member
Don't say Gravity.
Let's be sensible and take that as a given.

I mean what factors will cause bullet drop to be greater for one load than another.

My initial guesses are, from the same gun & calibre (eg .308), velocity and bullet weight and BC.

True? And, if so, what else?
 
Bullet Drop

Your question is so basic, I suspect there's another question coming. :confused:

Well anyway,
I've seen wind cause both drop and rise shooting 22LR targets.
 
Your question is so basic, I suspect there's another question coming.
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Not really.

A bullet starts to drop the second it leaves the barrel, but even at the same speed not all bullets will drop at the same rate, nor along the same trajectory.

I want to know if there are factors beyond those listed in the OP, that would have noteworthy effect on this....
 
Ballistics

In theory, if you were to drop an identical projectile from the same exact height and at the same exact time that the same projectile left the barrel of gun perfectly horizontal firearm, they would hit the ground at the same time. Old Newton here. Therefore based on the velocity that the projectile leaves the barrel that would be the single MOST critical criteria for the bullet drop. In theory the actual thing you drop would not even have to be equal in any way, but of course wind resistance for a feather is a lot greater than for a hunt of lead.

In real live things like wind resistance, sectional density, stability of the projectile (rifling rates etc.) certainly have an effect. Loss of mussel energy too when shooting longer distances for a given round.

For those that have a chronograph or access to one, set up on a bench and check the velocity close to the barrel, Then place the chronograph in front of your target at the distances that you normally shoot and shoot and see what the velocity is there. It will tell you a lot of expected performance at different ranges.

Bob
 
Bullet drop can be easily explained.
It's caused by our spinning and rotating planet and Newton's laws of physics.
Next question...
 
Pond said:
at the same speed not all bullets will drop at the same rate, nor along the same trajectory.
Click to expand...

All object "drop" at the same rate. How far they drop is dependent on the time they're allowed to drop. Bullets with lower BCs shed velocity quicker, so even if they have the same MV, they shed forward velocity faster than a bullet with a high BC. Generally, within a caliber, lighter bullets have lower BCs, so they shed forward velocity quicker than a heavier bullet. Their time of flight is therefore longer, and since they're allowed to drop longer, they drop farther.
 
In theory, if you were to drop an identical projectile from the same exact height and at the same exact time that the same projectile left the barrel of gun perfectly horizontal firearm, they would hit the ground at the same time. Old Newton here. Therefore based on the velocity that the projectile leaves the barrel that would be the single MOST critical criteria for the bullet drop. In theory the actual thing you drop would not even have to be equal in any way, but of course wind resistance for a feather is a lot greater than for a hunt of lead.
Click to expand...

All object "drop" at the same rate. How far they drop is dependent on the time they're allowed to drop. Bullets with lower BCs shed velocity quicker, so even if they have the same MV, they shed forward velocity faster than a bullet with a high BC. Generally, within a caliber, lighter bullets have lower BCs, so they shed forward velocity quicker than a heavier bullet. Their time of flight is therefore longer, and since they're allowed to drop longer, they drop farther.
Click to expand...

Nice answers!! Much clearer.
Thanks!
 
Yeah, I was under the impression all bullets drop at the same rate, the difference is velocity. A faster bullet fired at the same angle will travel farther before it hits the ground. BC is only a factor because it effects how quickly a projectile will slow down due to air resistance.
 
All object "drop" at the same rate. How far they drop is dependent on the time they're allowed to drop. Bullets with lower BCs shed velocity quicker, so even if they have the same MV, they shed forward velocity faster than a bullet with a high BC. Generally, within a caliber, lighter bullets have lower BCs, so they shed forward velocity quicker than a heavier bullet. Their time of flight is therefore longer, and since they're allowed to drop longer, they drop farther.
Click to expand...

That is it. I wrote the ballistics calculator for my Gun Log apps and had to learn about ballistics. I read a lot of papers, had to get out my college physics books and re-learn what I had forgot from college.

The amount of time an object is falling is directly related to how far it will fall. If you drop a basketball from your chest it will fall to the floor in less than a second. If you climb to the top of the empire state building and drop the basketball it will take longer than a second to hit the ground. The longer something is falling the further it falls.

If I shoot a bullet at 3000 fps with a ballistics coefficient (BC) of 0.5 it will take it .33 seconds to arrive at a target 300 yards way. If the bullet it only travelling 2800 fps it take is .36 seconds to get to 300 yards, that is 3 hundredths of a second longer. During that extra 300 hundredths of a second that is nearly 3" of more drop.

Maintaining speed is what the ballistics coefficient is all about. A bullet that cuts through the air better slows down less and maintains its speed, thus reducing the time to get to the target and thus dropping less because it was falling for less time.
 
All objects drop at the same rate in a vacuum.

In air, the objects drop at a rate determined by the interaction of gravity and the air resistance. Very dense objects (rocks, bullets) fall relatively fast, objects that aren't dense (feathers, Ping-Pong balls) fall more slowly.

If you have two bullets of the same size/shape, the one that is more dense will fall a tiny bit faster. HOWEVER, the difference isn't really significant since bullets are all pretty dense, they're all shaped about the same (in terms of the profile they present to the ground) and they usually aren't falling a long distance.

In practice, the only significant contributor to bullet drop is time of flight. If you have two identical bullets, the one that takes the longest to get to the target will drop the most. That's because gravity has more time to act on it. sirgilligan has it right.
 
James,

The answer to why and how fast bullets drop is simple - gravity.

All objects, even bullets, drop at the same rate regardless of weight.

With a bullet, the question may more precisely, how much drop will a bullet of a given weight and velocity drop over n yards'

The drop rate is identical with all bullets since they never achieve their terminal velocity in a downward direction unless they are shot straight up.
Then they achieve their terminal velocity on the way down.
However, a bullet traveling faster than another bullet towards a target will be covering the distance to the target in less time so it will be dropping less time before it hits the target. Therefore, it will have dropped less distance before it hits the target, so it appears that it drops less. The time it is in the air determines the amount of drop.

That is why there are "flat shooting bullets" like a .22-250 40 grain bullet that leaves the muzzle at over 4000 fps and bullets that shoot in big arcs like a 22LR that is travelling at 1100 fps out of the muzzle.
 
Just to add to the conversation, Ballstic Coefficient is a proxy for "drag."

A higher BC means less drag at any given velocity verses a bullet with a lower BC. The mass of the projectile actually has something to do with it as mass is resistance to force (force = mass*acceleration, therefore Force/Acceleration=mass).

Since drag is an acceleration dependent on velocity, more mass means more resistance to drag (generally expressed as more momentum).

But, if two bullets have the same BC and different masses, the lighter one will have less drop if it can be shot faster.

Hence the conventional wisdom of long range shooters, shoot the highest BC the fastest you accurately can.

Jimro
 
OK, so it really was that simply. Thanks for explaining, folks!

There is only one thing I have in common with sirgilligan: we had both completely forgot high school physics.. What separates us is that I didn't re-learn it!! :eek:

So really it now comes dow to velocity and drag that dictates where a bullet is at a given distance from the muzzle.
 
Saying gravity would be sensible
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Perhaps, then. But would it be helpful? ;)

What I did not know/remember was that the same thing drops at the same rate, but where depends on speed and drag and yet another day has passed when I've learnt something thanks to TFL.

TFL is good.

Pond likes TFL.
 
Mr. Pond,

Certain barrel conditions, a damaged grown for instance can cause the bullet to exit the barrel, in different orientations. It could be in any direction, depending upon where the crown is defective. If the defect causes deviation negative in the Y axis it could appear as greater drop, but gravity still would have the far greater effect.
 
You guys have it basically covered except you forgot that there can be variations in g. If I sight in my rifle down at my folks place and then go hunting on a long range shot I may well miss that deer because of the difference in g. The atmospheric pressure is less at higher elevations. You need to sight in at the elevation that you are going to hunt or shoot.
 
I may well miss that deer because of the difference in g.
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I've used that excuse for missing, as well as the "earthquake just as I was squeezing the trigger"

It would take a huge variation in gravity to make any measurable difference in the point of impact

Bullets fired LEVEL, from the same height, all have the same amount of drop.

The only difference is in the HORIZONTAL distance traveled before they hit the ground

But no one fires them on a level plane, so then it starts to get more complicated
 
You guys have it basically covered except you forgot that there can be variations in g. If I sight in my rifle down at my folks place and then go hunting on a long range shot I may well miss that deer because of the difference in g.
Click to expand...
You may miss the shot but it is unlikely that the miss would be because of differences in g. Those differences are small compared to the other trajectory changes induced by the different altitude. You would most likely miss because the thinner air presents less drag and the bullet doesn't slow down as fast. That would result in a shorter time of flight and therefore in less bullet drop.
The atmospheric pressure is less at higher elevations. You need to sight in at the elevation that you are going to hunt or shoot.
Click to expand...
This is correct. The difference in trajectory due to elevation changes is primarily due to the difference in air pressure (air density) which changes with altitude.
 
To confuse the issue just a bit:The drop begins from a presumed level barrel.We don't usually do that.As the bore is usually inclined,to place the bullet on target at zero 'd range,in effect the bullet is tossed up ,till it achieves maximum elevation at midrangetrajectory.("I sighted in 3.5 in high at 100 yds to put me on at 300)

So,actually drop does not begin until the time and distance have passed to put the bullet at the peak of trajectory.For a 300 yd zero,this may be at about 200 yds.At this point,drag has slowed the bullet,and the bullet will begin its drop from above the line of sight,by the height of the midrange trajectory.

We don't just drop the bullet,we give it a little toss up first.
 
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