Range Report Compensate for atmosphere difference between zero and current conditions

[ivelin]

I'm trying to build my own Excel-based point-mass solver using the McCoy's and Litz's books. I know there are very good ballistics apps but I just wanna know what exactly is happening under the hood and how they work. I think I got almost everything done but this.
I cannot figure out how exactly to compensate for air density difference from zero to current conditions.
Obviously, when the density is different, the muzzle velocity is difference and when the muzzle velocity is different, the zero range changes but what would the formula be?
What do I compare? Do I just get the difference between the air density at zeroing and current conditions and then change the zero range based on that or do I adjust the muzzle velocity or ..?

Nice forum by the way.

 

[Lowlight]

It doesn't change... for your zero to change it would take a lot more than any daily differences.

Example, I zeroed my rifle in CO at 8000DA and shot a match in Oregon at 2000 DA, my zero never changed and I never had to adjust it.

You need time & distance to work on the bullet, you don't have that time or distance at 100 yards...

 

[ivelin]

Thanks for the reply, Lowlight, much appriciated!

However, as I play with Ballistic AE app in my iPad for example (I compare my Excel solver against it) and put 8000DA for zero conditions and then use 2000DA for the current shooing conditions, the 100 yard zero no longer stays 0.00MOA in the trajectory table but it rather changes slightly to 0.02MOA which means that LOS is not longer zeroed at 100 yards but rather at ~99,8 yards. I know this my tiny but my point is, what does a ballistic calculator, exactly, do to compensate for that DA difference from condition at zero and at current. I'm trying to figure our the mathematics...

Thanks and sorry to bother if this is not the right place to ask!

 

[Lowlight]

Really, .02MOA and can you dial that ? ... what is your accuracy cone, maybe .5MOA so how do you know if its the conditions or the accuracy of the system.

Ridiculous to consider and bring up, especially when I see people will defer to decimals places you can't hold or adjust for. Hate to break it too but your trajectory goes from something like 78 yards to 109 with a 308, so you're gonna quibble over 2" of distance.

I don't care what anything says, if we have to drill down decimal places to prove the point you lost.

 

[ivelin]

No, no, of course that it is ridiculous to consider it in real world scenario, of course you can not dial that and of course we should not get down to decimals but remember, I'm trying to build a ballistic calculator in Excel and I trying to figure out how to calculate (compensate) mathematically for the difference between zero atmospheric conditions and current atmospheric conditions! At 100yards it may be just 0.02MOA difference, but at 1000 yards, I get up to 2-3 MOA and even more difference just because I have not compensated for atmospheric differences!

Thanks!

 

[EXTREMEPREJUDICE]

The Drag Equation There you go..............as the air density changes the drag function changes and as the drag function changes the trajectory changes. Your reference books have the other formulas you need (BC, trajectory, form factor, etc.)

 

[LastShot300]

No, no, of course that it is ridiculous to consider it in real world scenario, of course you can not dial that and of course we should not get down to decimals but remember, I'm trying to build a ballistic calculator in Excel and I trying to figure out how to calculate (compensate) mathematically for the difference between zero atmospheric conditions and current atmospheric conditions! At 100yards it may be just 0.02MOA difference, but at 1000 yards, I get up to 2-3 MOA and even more difference just because I have not compensated for atmospheric differences!

Thanks!

I think a good staring point could be the trajectory formula, the one involving the zero range. The Sierra Manual has some nice examples.

 

[Deleted member 10043]

Maybe you can cheat and use an Excel sheet already developed.

Ballistics programs and downloads

 

[ivelin]

I think a good staring point could be the trajectory formula, the one involving the zero range. The Sierra Manual has some nice examples.

Yes, I think that there should be some sort of comparison between the trajectory involving the zero range (with the zero atmospheric conditions) and the current one with current atmospheric conditions.
Thanks so much! Help much appreciated.

Maybe you can cheat and use an Excel sheet already developed.[/url]

Did not know there was such an Excel sheet already However, this one, I think, uses the Pejsa closed flat-fire solution where I'm trying to build a modern point-mass solver.
Nevertheless I'll check it out on how does this sheet compensate for the atmospheric differences.