Ballistic apps and potential energy via gravity

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Scotchmo

Scotchmo

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Jan 9, 2016
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I use Strelok and like it a lot, but since getting into ELR, I’ve been trying to get as precise as possible with my POI predictions. Strelok has a few mathematical issues that introduce small errors in the ELR predictions. There is one that I’m encountering lately. And it is present in other apps (ChairGun for instance) as well. Maybe there is some countering mechanism in the math that I’m not aware of, so that’s why it isn’t accounted for. If you like math/geometry/physics, you might be interested. After I explain it, let me know what you think.

This is a real example that I encounter at two different ranges.

Range (A) has a 600yd target down in a valley. -15 degree slope. That’s 466ft down.

Range (B) has a 600yd target up a hillside. +15 degree slope. That’s 466ft high.

Strelok (and ChairGun) show the same velocities and same required correction for both targets.

But a 105gr slug separated by 942ft of elevation has a difference of about 14 foot-pounds of potential energy. Certainly it took more energy to lift that projectile to the higher elevation. Where did that extra energy come from?

That should equate to a difference of about 30fps at the target. So why are they the same?

Instead of them both showing the same 104moa of needed correction, I would expect to see something like 106moa for the upward slope and 102moa for the downward slope. Am I wrong?
 
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Maybe...

...because that additional 30FPE of energy of the 942ft higher projectile is "positional" energy, potentially acting downward —
instead of "forward" or dynamic energy, actually hitting your steel plate with its force.

Since Strelok and ChairGun are ballistic calculators they try to focus on forward energy (not total energy) — because shooting is concerned with impact energy.


Just a thought....
I failed physics in high school — probably because the teacher refused to teach us ballistics and other exciting parts of our physical world.... 😉

Matthias 😊
 
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Closest data I found that would confirm your suspicion. With our sub-sonic projectiles I can definitely see gravity acting as either a brake (shooting up) vs coasting with gravity. (shooting downward)


1726803030153.png


1300 fps 240 grain even at 200 yards sees .38" differe3nce, so I imagine by 600, you'd experience quite a bit more at 1000~ fps with 105 gr.

-Matt
 
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JungleShooter said:
Maybe...

...because that additional 30FPE of energy of the 942ft higher projectile is "positional" energy, potentially acting downward —
instead of "forward" or dynamic energy, actually hitting your steel plate with its force.

Since Strelok and ChairGun are ballistic calculators they try to focus on forward energy (not total energy) — because shooting is concerned with impact energy.


Just a thought....
I failed physics in high school — probably because the teacher refused to teach us ballistics and other exciting parts of our physical world.... 😉

Matthias 😊
Click to expand...
That could be why they ignore it, but we also know that if we shoot straight up, the projectile will lose more velocity, than if we were to shoot straight down. Same thing for any target that is not horizontal, just to a lesser degree. At high angles, it becomes significant, so it can’t be ignored. I want to be able to predict a first round hit at 600yds, at any extreme angle that I might encounter. And I’d like to be able to rely on a convenient app like Strelok to take every significant variance into account, but currently, Strelok does not do that. Is there any app that does?

Note: It would also affect impact energy.
 
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Scotchmo said:
That could be why they ignore it, but we also know that if we shoot straight up, the projectile will lose more velocity, than if we were to shoot straight down. Same thing for any target that is not horizontal, just to a lesser degree. At high angles, it becomes significant, so it can’t be ignored. I want to be able to predict a first round hit at 600yds, at any extreme angle that I might encounter. And I’d like to be able to rely on a convenient app like Strelok to take every significant variance into account, but currently, Strelok does not do that. Is there any app that does?
Click to expand...

This one works for me if you're using slugs. At the least it does predict the difference between -15 and 15 degree angle shots.

play.google.com

Hornady - Apps on Google Play

Hornady Ballistics features advanced 4DOF trajectory and ballistic calculations
play.google.com play.google.com
 
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Stubbers said:
This one works for me if you're using slugs. At the least it does predict the difference between -15 and 15 degree angle shots.

play.google.com

Hornady - Apps on Google Play

Hornady Ballistics features advanced 4DOF trajectory and ballistic calculations
play.google.com play.google.com
Click to expand...
Thanks. I read through much of the Hornady documentation. It does take that very thing into account, along with some other things that I had also thought should be accounted for, including density changing as the projectile climbs or falls, during a high angle shot.

At least the changes in density partly counteracts the gravity affects.

Not sure if I want to change apps yet, but I’ll look at it some more.
 
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Scotchmo said:
Thanks. I read through much of the Hornady documentation. It does take that very thing into account, along with some other things that I I had also thought should be accounted for, including density changing as the projectile climbs or falls, during a high angle shot.

At least the changes in density partly counteracts the gravity affects.

Not sure if I want to change apps yet, but I’ll look at it some more.
Click to expand...

The only one I found that was free, the really, really nice ones cost 150-900$!

-Matt
 
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Scotchmo said:
I use Strelok and like it a lot, but since getting into ELR, I’ve been trying to get as precise as possible with my POI predictions. Strelok has a few mathematical issues that introduce small errors in the ELR predictions. There is one that I’m encountering lately. And it is present in other apps (ChairGun for instance) as well. Maybe there is some countering mechanism in the math that I’m not aware of, so that’s why it isn’t accounted for. If you like math/geometry/physics, you might be interested. After I explain it, let me know what you think.

This is a real example that I encounter at two different ranges.

Range (A) has a 600yd target down in a valley. -15 degree slope. That’s 466ft down.

Range (B) has a 600yd target up a hillside. +15 degree slope. That’s 466ft high.

Strelok (and ChairGun) show the same velocities and same required correction for both targets.

But a 105gr slug separated by 942ft of elevation has a difference of about 14 foot-pounds of potential energy. Certainly it took more energy to lift that projectile to the higher elevation. Where did that extra energy come from?

That should equate to a difference of about 30fps at the target. So why are they the same?

Instead of them both showing the same 104moa of needed correction, I would expect to see something like 106moa for the upward slope and 102moa for the downward slope. Am I wrong?
Click to expand...
If Range A and B are actually real ranges, not fictional ranges for example only, have you tried shooting on both?
If so, how did the results differ?
Edward
 
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Caliber 22 said:
Gravity act the same on both. Both will experience the same bullet drop. The difference in change of forward speed is so minimal that at rifle distance there will not be a practical difference.
Click to expand...

False, Scott was correct in his thinking and any very well equipped ballistic calculator will approximate these effects accurately.

You do not experience the same thing when you jump up 1-2 stairs versus jump down 1-2 stairs on a staircase personally, correct? Simple test to prove this theory, Earth's gravity is not biased. Jumping up 1-2 stairs requires more work than jumping down 1-2 stairs.

As he said, the increase in air resistance shooting down and decrease in air resistance shooting up slightly negates this effect, but not entirely, and this also depends on your initial elevation, and the angle of your shot. The greater the angle difference (-15 / +15 vs -45 / +45) the greater this effect. There is a chart above showing this exact effect at different angles and different ranges. The further the range, and the greater the angle, the more gravity effects the projectile, either to its benefit (less drop) or detriment (more drop).

-Matt
 
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SilentSquirrel said:
If Range A and B are actually real ranges, not fictional ranges for example only, have you tried shooting on both?
If so, how did the results differ?
Edward
Click to expand...
Yes. Real ranges. I have shot, or observed someone else shooting my rifles, all with my supplied dope, at both ranges. Not enough data to know. So far I haven’t decided if there’s any measurable benefit to accounting for it.
 
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Scotchmo said:
Yes. Real ranges. I have shot, or observed someone else shooting my rifles, all with my supplied dope, at both ranges. Not enough data to know. So far I haven’t decided if there’s any measurable benefit to accounting for it.
Click to expand...

The above chart is just one of many, but was the closest to sub-sonic they had, and those are not predicted, or calculated, rather real world results.

-Matt
 
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Stubbers said:
False, Scott was correct in his thinking and any very well equipped ballistic calculator will approximate these effects accurately.

You do not experience the same thing when you jump up 1-2 stairs versus jump down 1-2 stairs on a staircase personally, correct? Simple test to prove this theory, Earth's gravity is not biased. Jumping up 1-2 stairs requires more work than jumping down 1-2 stairs.

As he said, the increase in air resistance shooting down and decrease in air resistance shooting up slightly negates this effect, but not entirely, and this also depends on your initial elevation, and the angle of your shot. The greater the angle difference (-15 / +15 vs -45 / +45) the greater this effect. There is a chart above showing this exact effect at different angles and different ranges. The further the range, and the greater the angle, the more gravity effects the projectile, either to its benefit (less drop) or detriment (more drop).

-Matt
Click to expand...
You are very quick to call "false". As you stated with reference to that data you pulled from elsewhere, at 200y there is a difference of .38". Double that for 400y and double that again for 600y, then it is 1.5".

As I said, there is no PRACTICAL difference. Now, look at the target the OP shot at 600y.

1726923477175.png


That is a 25" x 23" plate. Good shooting at 600y. The OP did not say how many shots were taken, but I assume a lot more than what is on target, the rest are misses.

Now tell me, what contribute to the poi spread on that target? There are a lot of things we can speculate on and mention. Where exactly does the 1.5" difference between shooting up 15° or down 15° contribute to this poi spread and how do you determine which of the different factors is the main contributor of each poi. Does the horizontal distribution also result from shooting up or down?

Again, I say there is no PRACTICAL difference. Where is the "false" part in that?
 
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Caliber 22 said:
You are very quick to call "false". As you stated with reference to that data you pulled from elsewhere, at 200y there is a difference of .38". Double that for 400y and double that again for 600y, then it is 1.5".

As I said, there is no PRACTICAL difference. Now, look at the target the OP shot at 600y.

View attachment 497963

That is a 25" x 23" plate. Good shooting at 600y. The OP did not say how many shots were taken, but I assume a lot more than what is on target, the rest are misses.

Now tell me, what contribute to the poi spread on that target? There are a lot of things we can speculate on and mention. Where exactly does the 1.5" difference between shooting up 15° or down 15° contribute to this poi spread and how do you determine which of the different factors is the main contributor of each poi.

Again, I say there is no PRACTICAL difference. Where is the "false" part in that?
Click to expand...

Don't change your statement...you said "Gravity act the same on both." THAT is what is FALSE.

-Matt
 
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Caliber 22 said:
I did not change my statement. I now pointed out the one part of it.

As for gravity, as far as I know, unless something on earth changed, gravity acceleration is 9.81m/s/s. Is that different from shooting upwards than it is for shooting downwards?

Even then, on that target shown, which part of that poi spread is that 1.5" difference?
Click to expand...

Yes, because of the simple fact, when you're falling (or shooting downwards), Earth's gravity is accelerating you towards Earth, when you're jumping (or shooting upwards), your movement upwards, Earth's gravity is pulling you back to Earth....its not a difficult concept to understand.

The most extreme example would be, shooting directly up and trying to launch into space, versus shooting down from space onto earth...the projectile shooting up will lose its velocity at a great rate, while...falling down, the projectile will only decay to the point of terminal velocity based on Earth's Gravity...yes this is an extreme example, but it literally proves the point of how gravity will act differently based on your angle...90 degrees being the most extreme.

-Matt
 
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