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Dave King or JBM, Help! I found a ballistics problem!

 
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  #8  
Old 02-07-2005, 11:26 AM
JBM JBM is offline
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Re: Dave King or JBM, Help! I found a ballistics problem!

The elevation angle between the line of sight (what you see as you look through the sights/scope) and the barrel center line. This is the angle that you adjust when zeroing. Of course, this angle stays the same as you go to a higher elevation -- that's why you have to be able to input it.
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Old 02-07-2005, 11:34 AM
JBM JBM is offline
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Re: Dave King or JBM, Help! I found a ballistics problem!

[ QUOTE ]
Gravity stays the same. The only difference should be a "stretching out" of the parabolic curve due to higher retained velocities at higher elevations.

[/ QUOTE ]

The problem with this thinking is that there is a vertical component of the velocity that is retarded by gravity AND drag so with less drag it may go slightly higher -- less than an inch...
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Old 02-07-2005, 02:03 PM
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Re: Dave King or JBM, Help! I found a ballistics problem!

I don't have my Exbal PDA program right in front of me but, there's a check box somewhere in there that says "use field data". If this box is checked it will assume you've rezeroed at your current field conditions, and this would be closer to being zeroed at 300 yards than if it were using your original sight in conditions at lower altitude with the box unchecked.

I'll have to play with it a bit and see how mine's working.

I know you should see a remarkable change throught the trajectory curve if zeroed at sea level, use those sight in conditions then jump to 10,000' ASL.

POI may well be .5 MOA higher, so 2.25-2.50 MOA at 300 yards would now be more like it for a 300 yard zero.

The program should know what the total POI deviation from LOS would now be at whatever range. It knows the zero range, the atmospheric conditions at sight in and now in the field conditions and should modify the curve and resultant MOA correction at any range.

I wonder if the MOA correction Exbal gives on the calculate page matches the MOA correction in the drop chart page? Been a while now since I played with the program. Got to go locate my PDA come to think of it....
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  #11  
Old 02-07-2005, 03:00 PM
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Re: Dave King or JBM, Help! I found a ballistics problem!

I believe your right Brent-as stated. This is the reason I bought Exbal over all others.
My range is at SL in NC. I hunt in PA mountains, and do not re-zero. I don't have access to a range up there.
It's funny to me how many so called 'snipers' completely miss this. And how many 'sniper' marketed ballistic programs missed it as well.
Alot of assumptions I guess.
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  #12  
Old 02-07-2005, 10:34 PM
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Re: Dave King or JBM, Help! I found a ballistics problem!

Cool. This is all good. Let me know what you find.
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  #13  
Old 02-07-2005, 11:51 PM
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Re: Dave King or JBM, Help! I found a ballistics problem!

[ QUOTE ]
The problem with this thinking is that there is a vertical component of the velocity that is retarded by gravity AND drag so with less drag it may go slightly higher

[/ QUOTE ]

I stand corrected. Upon further consideration I agree that there is an upward inertia that is affected by the density of the air as the bullet lifts above the line of sight. A resistance from the atmosphere above the bullet. Thinner air means that gravity is increasingly responsible for pulling the bullet back down.

I still maintain my first writing is correct when the bullet is fired from a bore that is parallel to the line of sight (not that this would ever happen in the real world.) That is, a trajectory not intended to rise tward the line of sight.

I also maintain that the distance at which the bullet would now drop through the line of sight (the zero distance) would increase by yards and agree with you that the increase in rise would be teency weency.
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  #14  
Old 02-08-2005, 07:09 PM
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Re: Dave King or JBM, Help! I found a ballistics problem!

Your problem is exactly the reason I wrote a PDA program. If you have a Pocket PC you can get a beta version at http://biggameinfo.com/SureShotBeta.aspx. If you don't and want to play with the concept online try http://biggameinfo.com/BalCalcAdv.aspx, explore the SureShot tab after you enter your initial zero info.
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