Ballistic question on the effect of elevation and temp

Jaegerr

Lil-Rokslider
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Oct 19, 2024
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I'm in the process of setting up my rifle finally after some delay. I'm running a 7 PRC and opting to go with the Barnes 160 LRX factory loading out of personal preference. I was running a ballistic comparison between the roughly 5,000' elevation difference between where I live and where I hunt, and was wondering If I should use the drop chart for the higher elevation? An example being that if i set both charts to 200-yard zeros, the 100-yard impact would on the lower elevation is 1.41 inches - 0.39 mils, and the higher elevation is 1.31 inches - 0.36 mils.

My impact at 500 yard shows a 1.6-inch delta between the two, with the higher elevation with less drop even with factoring in a much lower assumed temp and humidity. As I don't live readily near a place I could shoot at that elevation to practice, would setting my zero down at low elevation to the assumed zero at high elevation work? That would have me hitting slightly low at 200 at the lower elevation when practicing right?

I also assumed a slight MV increase of 50 fps with the higher elevation, basing the 3000 FPS off the box 3050 FPS and my barrel being 22 inch and not the standard 24. Here is the link to the chart.

(I meant to add I doubt the small margin of difference at 100 will be distinguishable within any rifles cone of accuracy)

 
Site in at 100yd zero, dial up for 200yd if you want to walk around like that for quick shots. The 100yd zero won't change in a notable way at elevation, make your adjustments from there with the enviromentals.

Off the box muzzle velocity means nothing if you are talking 500yd, you need to prove out your velocity (with true drops and/or chrono).
 
How do you propose to zero your rifle differently to account for elevation when there is a 0.09 MOA difference between the 2 at 100 yards and your scope either has a .25 MOA or 0.36 MOA sized adjustment?

Guessing off a velocity on a box and for distances you've never shot isn't a good plan. Beyond about 300 yards sounds like too far.
 
Zero at 100 WELL, true your dope out to your maximum range. Yes, the 5000' elevation difference will afftect your dope, any ballistic app will adjust that for you if you plug in enironmentals. But you seem to be seeing .03mil--less than one half of .1 mil--at 100 yards, so it is correctly telling you that your zero would not change. 1.6" at 500 yards is less than .1 mils. I would worry a lot more about having a perfect zero and truing your actual dope, than I would about a .1mil shift at 500 yards.
 
You're way overcomplicating it. A functional 100 yard zero is more precise and good at any elevation. Now that I have a rangefinder with sensors and a solver I much prefer exact solutions, but in your case I would recommend the following:
- Establish a large sample 100 yard zero.
- True up a ballistic solver by actually shooting targets at ranges you intend to shoot.
- Input the elevation and environmentals of your hunting location and formulate a drop chart.

Take into consideration this won't account for variables like shot angle, or powder temp sensitivity.

OR, spend $200 and buy a Sig Kilo 3k on sale that has AB-U, and true up a profile so you have a solver in hand and don't have to worry about any of it.
 
There's a lot to unpack there and not enough info to really do it.

What's the actual longest range you have regularly shot this rifle/load with on your home range on any sort of regular basis this summer?
 
Site in at 100yd zero, dial up for 200yd if you want to walk around like that for quick shots. The 100yd zero won't change in a notable way at elevation, make your adjustments from there with the enviromentals.

Off the box muzzle velocity means nothing if you are talking 500yd, you need to prove out your velocity (with true drops and/or chrono).
I plan on ordering the athlon chrono this week
 
There's a lot to unpack there and not enough info to really do it.

What's the actual longest range you have regularly shot this rifle/load with on your home range on any sort of regular basis this summer?
Not this rifle but others at 550
 
You're way overcomplicating it. A functional 100 yard zero is more precise and good at any elevation. Now that I have a rangefinder with sensors and a solver I much prefer exact solutions, but in your case I would recommend the following:
- Establish a large sample 100 yard zero.
- True up a ballistic solver by actually shooting targets at ranges you intend to shoot.
- Input the elevation and environmentals of your hunting location and formulate a drop chart.

Take into consideration this won't account for variables like shot angle, or powder temp sensitivity.

OR, spend $200 and buy a Sig Kilo 3k on sale that has AB-U, and true up a profile so you have a solver in hand and don't have to worry about any of it.
I'm working off of my razor 4000 without GB, but I'll have dope chart once I get it shaken out on my rifle and lock screen.
 
I plan on ordering the athlon chrono this week
The really short answer to what should be a really long discussion, is that you can trust a good ballistics app to give you good info after you put good info into it. That includes info about how elevation will change your trajectory. But you need to go chrono your ammo and verify your trajectory out to your max range.

Brutal honesty here - I have never seen data verified at 500 yards fall apart at 600 yards. But I have seen data verified at 600 fall apart at 1000, or verified at 750 fall apart at 1250. I think with better bullets and better tips and more honest BC figures and scopes that actually track it's less of an issue now than it used to be, but there's no way on earth I'd go lobbing bullets at stuff at 500 yards until I'd seen my rifle do what the app says, and certainly NEVER based on a 200-yard zero. Or even 300. When I was younger I wasted a lot of ammo believing published trajectory charts and published BCs and published velocity figures. And even now I still shoot muzzleloaders and .22lr and other lower-BC stuff at 100-300 yards a lot and I don't trust anything until I see hits on steel.
 
The really short answer to what should be a really long discussion, is that you can trust a good ballistics app to give you good info after you put good info into it. That includes info about how elevation will change your trajectory. But you need to go chrono your ammo and verify your trajectory out to your max range.

Brutal honesty here - I have never seen data verified at 500 yards fall apart at 600 yards. But I have seen data verified at 600 fall apart at 1000, or verified at 750 fall apart at 1250. I think with better bullets and better tips and more honest BC figures and scopes that actually track it's less of an issue now than it used to be, but there's no way on earth I'd go lobbing bullets at stuff at 500 yards until I'd seen my rifle do what the app says, and certainly NEVER based on a 200-yard zero. Or even 300. When I was younger I wasted a lot of ammo believing published trajectory charts and published BCs and published velocity figures. And even now I still shoot muzzleloaders and .22lr and other lower-BC stuff at 100-300 yards a lot and I don't trust anything until I see hits on steel.
Noted. I appreciate the wisdom then, and I can understand the trust but verify mentality. I'll start at a basic 100 yard zero and step out to 500~ yards. I have not taken shots outside the 5–600-yard range, so that's my self-imposed max range.
 
100 yard zero, dial on “walking around maximum point blank zero” if you want.

Verify the dope in your ballistic calculator with proper environmental data entered at your home range.

Then in new conditions, update the environmentals in ballistic calculator.

You won’t miss because of calculation error with new environmentals out to 500-600.

You will miss more because of wind or wonky field positions you don’t practice. The biggest source of elevation error I see in the field is lack of recoil management. It affects me too. It’s why I “gamed” it by shooting smaller calibers.

It’s not a dig on you, but the above is reality for the vast majority of the shooters that I meet up with to help. Especially when you are asking a good question, it shows you are trying to learn and figure things out. The internet is confusing. Hope this helps
 
100 yard zero, dial on “walking around maximum point blank zero” if you want.

Verify the dope in your ballistic calculator with proper environmental data entered at your home range.

Then in new conditions, update the environmentals in ballistic calculator.

You won’t miss because of calculation error with new environmentals out to 500-600.

You will miss more because of wind or wonky field positions you don’t practice. The biggest source of elevation error I see in the field is lack of recoil management. It affects me too. It’s why I “gamed” it by shooting smaller calibers.

It’s not a dig on you, but the above is reality for the vast majority of the shooters that I meet up with to help. Especially when you are asking a good question, it shows you are trying to learn and figure things out. The internet is confusing. Hope this helps
Absolutely no hard feelings here. I’ve asked some silly questions on here in an effort to help establish fundamentals and basics that are rock solid. I’d rather ask the question and get told I’m wrong than arrogantly assume I’m right!
 
I'm working off of my razor 4000 without GB, but I'll have dope chart once I get it shaken out on my rifle and lock screen.
Many people print dope charts for different DA, which is set by temp/station pressure. You can have some pre-printed for the days you will be sent out. Or, you can do a screenshot for the expected environmentals of the day.
 
Many people print dope charts for different DA, which is set by temp/station pressure. You can have some pre-printed for the days you will be sent out. Or, you can do a screenshot for the expected environmentals of the day.
Sorry, DA?
 
Density Altitude, it is one number using temp, station pressure (actual air pressure--not barometric pressure which is normalized based on elevation) and humidity (which is so minimal it can be set at 50%)
 
Sorry, DA?
Some apps use DA, some use temp/pressure. You have to be careful to not use 'adjusted pressure'. If a weather forecast at 8,000' tells you the local barometer is at 30.5 for the day.....that's adjusted. The actual pressure at 8000' is going to be much closer to 21.5-23mmHG.

You can make either method work fine, you just have to have good info.

What *range* of elevations will you be hunting? Expected temps?

Cold air is denser. Higher elevation air is thinner. Really cold air at 8000' is thicker than much warmer air at 11,000' but as a very general, vague, dangerous sort of rule, if you were going to shoot 100% inside of 500 yards and might see an elevation range of no more than, say, 8k to 11k, and a temperature range of no more than, say, 20F to 55F, you could run a single set of numbers at maybe 9500' and 40F, and they would *probably* be well within minute-of-elk for whatever conditions you might encounter.

But again that's a dangerous rule without knowing a whole lot of the assumptions you're going to build your dope on.
 
Some apps use DA, some use temp/pressure. You have to be careful to not use 'adjusted pressure'. If a weather forecast at 8,000' tells you the local barometer is at 30.5 for the day.....that's adjusted. The actual pressure at 8000' is going to be much closer to 21.5-23mmHG.

You can make either method work fine, you just have to have good info.

What *range* of elevations will you be hunting? Expected temps?

Cold air is denser. Higher elevation air is thinner. Really cold air at 8000' is thicker than much warmer air at 11,000' but as a very general, vague, dangerous sort of rule, if you were going to shoot 100% inside of 500 yards and might see an elevation range of no more than, say, 8k to 11k, and a temperature range of no more than, say, 20F to 55F, you could run a single set of numbers at maybe 9500' and 40F, and they would *probably* be well within minute-of-elk for whatever conditions you might encounter.

But again that's a dangerous rule without knowing a whole lot of the assumptions you're going to build your dope on.
Southern Montana, low side 4,000 and high side I’d guess 8,000? It’ll be an early November hunt so the peaks are at 11k~ but I imagine from my limited knowledge elk will be pushed lower if it starts snowing early this year. That’s what lead me to the 5k elevation assumption, maybe should use 6k as median value.
 
Southern Montana, low side 4,000 and high side I’d guess 8,000? It’ll be an early November hunt so the peaks are at 11k~ but I imagine from my limited knowledge elk will be pushed lower if it starts snowing early this year. That’s what lead me to the 5k elevation assumption, maybe should use 6k as median value.
Run ballistics daily based on the temp and elevation and screen shot it. Also, when glassing, you can update it as you are also reading wind.

Don’t get wrapped around the axle.

It’s why I just bought into the AB universe and have it on my phone, binos, and Garmin. Keep it simple on the mountain…
 
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