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Incline shooting at ELR, Apps give different results?

 
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  #1  
Old 09-17-2012, 03:42 AM
M67 M67 is offline
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Incline shooting at ELR, Apps give different results?

I am planning a shot @about2km. The shot is about 20degrees up, this is a learning shot - and i will try to analyse it beforehand instead of afterwards, to see if it helps hit probability. I have done very little shooting past 1500m, not much past 1300m really. Inside 1300m i have shot quite a bit, and i would expect to hit an elks vitals at 1200m i someone handed me the shot here and now. Elevation was spot on at 1285m last weekend, so i do have some control over my shooting (just to make that clear)
@1500m i experience good repeatability and accuracy

The load is the 300gr Berger OTM bullet, Initial velocity is 826m/s, BC G7=.419
Met&env
pressure at firing point 1000hPa, pressure at impact point 915hPa
temp at firing point 13 degrees C (expected temp at impact point 7degrees C
direction of fire 270degrees (due west),
position is at 66degree north

I was wondering what to enter in the program, firing pos pressure and temp, or average temp and press.? Do the programs correct for these things automatically or what goes on?

Earlier i have seen a click or two discrepancies between Bulletflight and Shooter (Iphone), Shooter beeing "best" @ ranges >1000m, past 1000 but that may also be a sight in-issue.
For some incline shooting practice this summer i shot out to 800m, and inclines to 51 degrees - using Bulletflight because i feel it is easier than Shooter, and less prone to operator error. Having the luxury of shooting in absolutely still conditions, at night, in full daylight, everything was spot on - i was happy... (a digression)

Anyway, the 2k shot:
_______Shooter ___Bulletflight ___Difference BF/Sh.
flat ____31.1 ______30.7________ 5
20_____29.4______29.6_________-2
-20 ____28.9______28.0_________9

In Bulletflight the flat-fire bullet arrives with 309m/s, but in Shoooter it is 302. Both programs give .2 mils of extra elevation for Coriolis, and 1.0 sideways for spin+Coriolis. For 10m/s of wind they are within .1mil (9.9vs10.0)

Now how is that for difference in elevation? Shooter has .5mils of difference between up and down, but Bulletflight has 1.6!
Obviously one program corrects more than the other, and one must be more correct than the other? I suspect the largest correction to be correct?

Has anyone experience with this? Could some with real ballistic knowledge chime in? Please do not bring in any riflemans rule/cos distance stuff - it simply does not work, even @ 500m.

K
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  #2  
Old 09-17-2012, 06:50 AM
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Re: Incline shooting at ELR, Apps give different results?

I use the temp/pressure where I am.

Have you aligned your ballistic program with your load? Also what is your optic?
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  #3  
Old 09-17-2012, 08:53 AM
M67 M67 is offline
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Re: Incline shooting at ELR, Apps give different results?

Alignment

I have fired in exess of 2000 rounds @LR in 2012, about 4000 rounds total this far 2012. I logged 24 shooting sessions @ ranges >1km.
For my 6.5x55 i use two different profiles (instead of banded BCs, i do use G7 BCs) one is spot on to about 900m and use the Litz automatic BC, from 600-1500m i use a different BC .295
In the 338LM i use .419 in Bulletflight, and auto in Shooter - the goddamned program wont let me see it which is a hindrance...

There is full consistency between chronographed (over more than a year) velocities, and reverse-engineered velocities made from drop values. the 6.5x55 barrel has 4200 rds. down it and shows a steady decline in velocity.

Using both apps, or my logbook, i would expect to make 1. round hits on any sensible target to at least 1200m, give or take wind.

Optics
My 6.5x55 and 223 LR rifles both have Vortex Razor HD 5-20x50 scopes, the 338 has a IOR 3.5-18x50 MP8 FFP SH WTF scope and my .22LR "silent practice" rifle has a March 3-24x42. None of the scopes has ever given me any issues to click value, repeatabilty or tracking.

Original question
None of the above has anything to do with the question:

Why do the apps give significantly different predictions?

In addition to the things considering when shooting flat (well it must be for total accuracy, og when the arc of the bullet is high enough, as in artillery proper) is:
- gravity acting along bullet path
- density change due to different pressure along bullet path
- density change due to different temperature along bullet path
at least...

do the apps consider these things, and others?

K
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Old 09-17-2012, 08:08 PM
LR3 LR3 is offline
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Re: Incline shooting at ELR, Apps give different results?

At best I think of the programs as approximations of the truth, just like statistics. I use Exbal and FFS on nomad. I was told they use different drag corrections and in the case of Ffs this can be matched to the actual ballistics. Beyond a mile I think the variables get very difficult to take fully into account but you seem to have much of that knowledge. On this site many recommend cold bore shots. I suspect it would be better to fire a shot to warm the barrel like with bench rest and then do a ranging shot about 100 yds to one side at those extremes ranges. I doubt you ll find a program that can repeatdely predict what you want with accuracy of .3 moa at 2000m with varying weather conditions. I can get predictions to correlate to about 1 to 2 Moa on the vertical but horizontal is more difficult. I use a vectronics for incline input. Good luck and let us know if you find an answer.
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Old 09-18-2012, 01:48 AM
M67 M67 is offline
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Re: Incline shooting at ELR, Apps give different results?

As i understand the theory of ballistics, it is an absolute science. When all forces are accounted for, and all input variables are correct - the result is, in principle that theory reflects reality exactly.
The routines in the apps and programs, use very accurate mathematics to integrate the equations of motion. They are all pointmass solutions, so any effect caused by pitch or yaw, such as drift, are pure approximations, curve fits if you want.
But the trajectory as ruled by gravity is not, nor is aerodynamics - save for the drag function, that is a fit to the G7 drag function, scaled to the actual bullet.
As bullets are individual, this is generally not 100% accurate, as the input variables are not 100% accurate, (like which temperature to enter) the solutions is not 100% accurate, and the gravitational constant and other "constants" in the program may not be 100% accurate.
And not all effects that take place in reality is accounted for in all theory, something may be left out for ease of computation, or other reasons.

What i am after is to know what, specifically what does Shooter and Bulletflight take into account, and not? Maybe do they use different versions of the G7 dragfunction? Or are one using a more detailed approach?

I have found, as far as i can shoot "accurately", measuring carefully and enter all the program asks for correctly, AND fiddle the BC to the bullet, predictions as scary accurate thereafter - as in 0.1mil (one click). A friend of mine more or less shoots and hunts full time, and even he cannot repeat the same shot much more accurate - an at 12-1400m hitting within one click is fine by me.

This constitutes the difference between thery and practice if you wish - it can be minimised, but it is there. Difference between theory and theory is more concerning, for it cannot be minimised by the user. The example i use have the two programs differing by almost a full milliradian, that is 2meters, four feet - two g..mn yards - and i am certain the modelling accuracy within the mathematical routine is more accurate than that.


K
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Old 09-20-2012, 11:44 AM
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Re: Incline shooting at ELR, Apps give different results?

Shooter accounts for the difference in air density along an inclined shot. I don't know for sure if Bullet flight does this, but based on your comparison of the results, I would guess it doesn't. here's why:

On the look-up shot, the Shooter solution calls for less elevation than Bullet Flight. This is consistent with the bullet flying thru thinner air as it goes up in altitude. The opposite is true of the look down shot.

Having said that, I also don't know the exact details of the rest of BulletFlight's calculations, so the comparison could be explained by something else.

What I can say for sure is that Shooter calculates the variation in air density along the trajectory based on conditions at your altitude, so you don't have to average (mentally or otherwise) the altitude/pressure along the trajectory.

Very interested in hearing about your results.

Good shooting,
-Bryan
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Old 09-20-2012, 03:59 PM
M67 M67 is offline
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Re: Incline shooting at ELR, Apps give different results?

Quote:
Shooter accounts for the difference in air density along an inclined shot.
Thank you, this is good info for sure. Still there is 0.4 mrad between the programs but i'll triple check my variables and shoot, before i complain on that. Yrcan on the forum probably will chime in, as he is out to do some ELR and incline confirmation shots, as we speak more or less.
Hopefully we will both put Bryans big OTM bullets in red deer during the weekend too. Good Times

Quote:
I don't know for sure if Bullet flight does this
It does not. I emailed Robert Silvers, and he confirmed Bulletflight does not. Ballistics by Jonathan Zdziarski does not either, since it returns a very similar result to Bulletflight.

On the other hand Ballistics have a very neat wind-drift judging tool, that i spent all of yesterday evening playing with, and comparing to some shooting i did earlier this fall, across a valley, with near and far wind opposite - and vertical wind to boot. Ballistics neatly predicted the effect of lift on the hill, lift that i saw, but could not quantify into clicks on the scope at the time. Neat

So now we have Ballistics with a neat wind-tool, Bulletflight for stone-proof bug free and foolproof operation, and Shooter for loong inclined shots and movers... I say -

K
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