Help with some ballistics

[Tater1985]

So my wife and I will be leaving for an elk hunt in WY in about a month. I had put a 300 WM barrel on my Encore this spring and started load development with 180gr Accubonds and H1000. I found a load that worked well in the gun, and have loaded up enough ammo for practice and the hunt.

This past weekend I was actually able to test it at various distances and try my making adjustments to my CDS dial on my VX3. I have the rifle zeroed at 200yds and was able to shoot out to 550 yds to confirm that the data from the ballistics calculators was infact correct. I have been playing with the following calculators:

Strelok (on my phone)
G7 (web based)
Pejsa (jacksons ballistics, excel spreadsheet)

They all seemed to be within 0.2-0.3 MOA at 550yds when using my "HOME" data:

Elev 800ft
Temp 85 F
MV 3011fps
Hum 50%
Pres 30.00

But when I try to put in what I am being told will be average conditions for my hunt, they are varying quite a bit.

Elev 8000ft
Temp 50 F
MV 3011fps (used same, mainly out of ignorance)
Hum 50%
Pres 30.00

These are the MOA corrections I get for 550yds:

Pejsa – 7.8 MOA
G7 – 8.7 MOA
Strelok – 9.9 MOA

Can anyone point me in the right direction? I was quite pleased that all the calculators were reasonably close with my home data, and that's what I tested over the weekend, but now that I try to change the temp and altitude, they are all over the place. What am I missing?

 

[RTK]

Does the program use station pressure or altitude pressure?

 

[Tater1985]

I think each of the program's is a little bit different I know they all have a place to put in the altitude and to put in the pressure but I'm thinking that this must be a corrected pressure something that I did not know anything about but read a little bit about it after I posted this question I think this may be the main reason I'm getting such a variance.

The ballistic app on my phone has a place to input the altitude temperature and pressure or you can click a radio button to automatically select standard pressure and temperature for that altitude I'm wondering if I wouldn't be better off to select that option and then just alter the temperature box for each altitude and location that I'm trying to get info for?

 

[DocUSMCRetired]

Your pressure is not going to be the same. It is not going to be perfect, but you can give about .354 per 1000 feet.

 

[Tater1985]

Your pressure is not going to be the same. It is not going to be perfect, but you can give about .354 per 1000 feet.

Doc,

Are you saying subtract .354 per 1000ft from the pressure I used at home? I have been using 30.00 as kind of an average pressure here at home (800ft). So if i plan to hunt at 8000ft, the difference would be 7200ft. So .354 x 7.2 = 2.55 . . . . . . . . 30.00 - 2.55 = 27.45.

Please let me know if i misunderstood.

 

[DocUSMCRetired]

Doc,

Are you saying subtract .354 per 1000ft from the pressure I used at home? I have been using 30.00 as kind of an average pressure here at home (800ft). So if i plan to hunt at 8000ft, the difference would be 7200ft. So .354 x 7.2 = 2.55 . . . . . . . . 30.00 - 2.55 = 27.45.

Please let me know if i misunderstood.

If you are starting at 800 feet, then I would start at 29.667 pressure (station pressure), then subtract .354 for every 1000 feet. Because sea level is 29.95. This is not going to be near exact, but much better than running 30.00. It is not as accurate the farther you go from sea level, and this is station pressure not barometric. But it can help get you an idea of what you are looking at. Nothing is going to beat using the full on formula, or doing the research on where you will be. The best way, would be to use a Kestrel Elite, or Drop 3. But if we have to guess, this will let you guess. Just understand its flawed. But you have the right idea. Its better than using 30.00.

 

[Tater1985]

So i tried using Docs approach in various calculators and im still getting varied results. Some say i need more clicks at a given range and others saying i need less.

 

[Greyfox]

I have experienced the same problem of entering identical inputs into different ballistic programs and getting different results. Actual field testing to 1200 yards for several different hunting rifles/loads over the years has helped me to settle on a few programs that I can use that give identical outputs for "correct" and identical inputs , and can be relied upon to put the bullet where it's supposed to go. Perhaps I may be doing something incorrect with some programs, but I do believe that not all ballistic programs are created equal even though they claim to use common algorithms. I think it's up to the shooter to find the ballistic program that works for them. IMO.

 

[DocUSMCRetired]

I have experienced the same problem of entering identical inputs into different ballistic programs and getting different results. Actual field testing to 1200 yards for several different hunting rifles/loads over the years has helped me to settle on a few programs that I can use that give identical outputs for "correct" and identical inputs , and can be relied upon to put the bullet where it's supposed to go. Perhaps I may be doing something incorrect with some programs, but I do believe that not all ballistic programs are created equal even though they claim to use common algorithms. I think it's up to the shooter to find the ballistic program that works for them. IMO.

You are correct, they are not all exactly the same. Some account for more than others, and not all of them treat wind the same etc.