Ballistic apps and potential energy via gravity

[Scotchmo]

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?

 

[JungleShooter]

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

 

[Stubbers]

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)

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

 

[Scotchmo]

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

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.

 

[Stubbers]

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?

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.

Hornady - Apps on Google Play

Hornady Ballistics features advanced 4DOF trajectory and ballistic calculations

play.google.com

 

[Scotchmo]

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.

Hornady - Apps on Google Play

Hornady Ballistics features advanced 4DOF trajectory and ballistic calculations

play.google.com

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.

 

[Stubbers]

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.

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

-Matt

 

[SilentSquirrel]

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?

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

 

[Caliber 22]

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.

 

[Stubbers]

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.

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

 

[Scotchmo]

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

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.

 

[Stubbers]

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.

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