elevation

[velvetant]

So does elevation effect groups?
I recently moved to Missouri from northern Nevada. I did load work up in Nevada and was consistently shooting under
half inch groups. Nevada 6000ft, Missouri 800ft.
Now I'm lucky if I can keep them under and inch.
These are loads that I loaded in Nevada and are the same lot as I'm shooting here.
The only thing that changed is moving across country.
I'm puzzled......
This if for my 6.5Creedmoor
Should I start by playing with seating depth?

 

[Kodiak]

Possibly the humidity was lower in NV and its in the 50-60% around the midwest area. I reside near the Mississippi River and its not uncommon for it to be 70%. Loads I develope here do not perform well in the dry climate of eastern Montana, where I participate on some long-range (800-1000 yd.) rifle matches.

Something to consider, but I'm sure there are other folks that hang-out here that will have input!

 

[DrMike]

Elevation does have an impact on group size.

 

[Oldtrader3]

I think that the change in relative humidity as one goes higher would explain most of the group shift. Plus the air becomes less dense at higher altitude.

 

[nvbroncrider]

Yeah humidity is way lower here in the summer the average day ranges from 6-22% in the fall 20-45% winter will climb a little 30-60% plus the change in elevation I wouldn't be surprised if you need to tweak it.

 

[Elkman]

I know that the point of impact will change, but have not seen data regarding group size. I have not seen that myself. Just my 02

 

[FOTIS]

Yes and humidity and baro pressure etc.

 

[Horsethief]

Several months ago Craig Boddington wrote a great article in Rifle Shooter Magazine.
http://www.rifleshootermag.com/2013/09/ ... ct-rifles/

Boddington's words are summarized below.
For every 20 degrees Fahrenheit cooler than the difference of the temperature at which you zeroed, expect a difference of 0.5 to 1 MOA. Heat has the exact opposite effect, with the same rule of thumb being an increase of 0.5 to 1 MOA for every 20 degrees warmer than your sight-in temperature.

For every 5,000 feet of elevation difference between your sight-in elevation and the elevation at which you are hunting, you can expect (you guessed it) 0.5 to 1 MOA difference. As you increase elevation, your point of impact will rise (all other things being the same).

You can expect about a 0.5 MOA change for every 20 percent change in humidity. Moist air is less dense than dry air, so if you go from a desert climate to an area with high humidity you can actually expect your point of impact to rise.

 

[Elkman]

Elevation does have an impact on group size.

I already know that environmental factors effect trajectory, but the question was "group size". How does elevation, or temperature or humidity, effect it? Can't one assume that "all" of the rounds with the same components will be effected the same????? I am still not getting this at all.

 

[Vince]

Several months ago Craig Boddington wrote a great article in Rifle Shooter Magazine.
http://www.rifleshootermag.com/2013/09/ ... ct-rifles/

Boddington's words are summarized below.
For every 20 degrees Fahrenheit cooler than the difference of the temperature at which you zeroed, expect a difference of 0.5 to 1 MOA. Heat has the exact opposite effect, with the same rule of thumb being an increase of 0.5 to 1 MOA for every 20 degrees warmer than your sight-in temperature.

For every 5,000 feet of elevation difference between your sight-in elevation and the elevation at which you are hunting, you can expect (you guessed it) 0.5 to 1 MOA difference. As you increase elevation, your point of impact will rise (all other things being the same).

You can expect about a 0.5 MOA change for every 20 percent change in humidity. Moist air is less dense than dry air, so if you go from a desert climate to an area with high humidity you can actually expect your point of impact to rise.

Thank you Horsethief!
The info I was looking for was right there thanks to your most generous use of the linking url.
Vince

 

[Elkman]

At long last some definitive info. I information. I wonder if it's cumulative. For instance if all three. Are different will it add up the changes ? When I wake up in the morning I will visit this again. At this time it seems that load development needs to done at elevation and cold weather. H mmmmmmmmm thanks all I have been pondering o PM this for quite some time.

originally penned by Bill "under medication" at 0300 this am.

 

[Oldtrader3]

Bill, each of these is an independent variable. They have nothing to do with one another except to the extent that temperature may drop at high altitude.

 

[Elkman]

Morning Charlie
My mind is a lot more clear this am. I think most were aware of the effect that altitude has. It has been the humidity and temperature that I could not get my mind around. Still can,t but wii except the information. Seems as though for the long range hunters that final load development should be made at as close to hunting conditions as possible. I have always ran two range cards for elevation but other than for drop, I did not factor in a change in group size as the humidity and temp changed. Seems as a lot more load development needs to take place in weather corresponding to hunting conditions. Hnmmmmmmmm

 

[wildgene]

Bill, I've got the Sierra Infinity that allows you to input BP, temp, alt., humidity, etc. They all add up, or add & subtract, but the lower the elev. the more effect (more/ denser air)...

 

[Elkman]

Thank you gene, I want to run a few ballistics, calculations at say 600 yards, to see how much the changes may be for the medium range hunter. I am guessing that up to 600 a small differences wil make very little changes. Out farther however I am sure they are huge. Might take me a few days as I start physical therapy this week. I will run say temp at, 300, 600, 900' 1200 and see. I know we have computers that wii do this for us. But I will learn more if I understand the parameters, and how they correlate. It interests me greatly.

 

[wildgene]

Thank you gene, I want to run a few ballistics, calculations at say 600 yards, to see how much the changes may be for the medium range hunter. I am guessing that up to 600 a small differences wil make very little changes. Out farther however I am sure they are huge. Might take me a few days as I start physical therapy this week. I will run say temp at, 300, 600, 900' 1200 and see. I know we have computers that wii do this for us. But I will learn more if I understand the parameters, and how they correlate. It interests me greatly.

...I believe they all are an effect of air density, colder air/ more dense, higher elev./ less dense, higher humidity/ more dense, but the colder the air the less moisture it will hold so 10* air w/ 90% humidity probably holds a lot less moisture than 80* air @ 60%. I do believe they are all relevant, but in most cases it would take a considerable dist. & degree of accuracy to measure their individual effects. I think you'll see the most direct effect from elev. Temp. is also a concern, but more from it's effect on MV's/ powder burn rate...

...kinda like you start out w/ "a" (200yd. "Zero" @ 5800ft. elev./ 43*/ 58% humidity) + "e" (8000'ft. elev.) - "t" (15*) - "h" (85%) = "a" +/- 1-3%...

...it still all boils down to despite our best efforts, it's still all a "guestimate", but the better our data, the closer the "guestimate" is to reality...

 

[Elkman]

Gene
...it still all boils down to despite our best efforts, it's still all a "guestimate", but the better our data, the closer the "guestimate" is to reality...

zackley ! And the better I school myself, hopefully the better I will learn.

 

[Vince]

Gene
...it still all boils down to despite our best efforts, it's still all a "guestimate", but the better our data, the closer the "guestimate" is to reality...

zackley ! And the better I school myself, hopefully the better I will learn.

I'm always up for learnin' me sumppin new that's relevant to my endeavors. :grin:

I've seen elevation effect my POA/POI but have yet to play with temp and humidity.

 

[Horsethief]

While all these things can add up to something that makes a difference, what isn't accounted for directly is the mirage distorting the target. A great load developed to the best degree can go south fast when a difficult mirage shows its ugly face.

Years ago I kind of had the knack for reading the mirage @ 600 yards, but we were using iron sights so the mirage didn't appear to be as bad as it would have been with today's optics.

Probably the worst combination is when wind gusts become difficult to measure coupled with a bad mirage.

 

[wildgene]

Gene
...it still all boils down to despite our best efforts, it's still all a "guestimate", but the better our data, the closer the "guestimate" is to reality...

zackley ! And the better I school myself, hopefully the better I will learn.

I'm always up for learnin' me sumppin new that's relevant to my endeavors. :grin:

I've seen elevation effect my POA/POI but have yet to play with temp and humidity.

...ok, well, let me throw just a few more things @ you that might be of concern. Density altitude which is elev./ temp./ humidity's effect on the density/ resistance of the air you're shooting thru, & ToF (time of flight), because the longer the air has to interact w/ the bullet, the greater the effect. As I mentioned before it's going to require a substantial difference in environment, & exceptional accuracy to notice the actual change in trajectory. A couple of things that would probably be much more noticeable would be scope adjustments & parallax. Most scopes, even the better ones, seem to show a difference in the amount of actual adjustment as you move farther from the true center towards the ends of the adjustment range. A scope that shows perfect 1/4 MOA clicks thru the first 20 might be substantially short out past 20 MOA, only way to know is to physically check it. Most of us won't have the luxury to set out an 8'X8' target @ transonic range, but if you tables tell you 8.6 MOA & your scope says 10, I'd go w/ the scope. The other, parallax, adjust your ocular objective to get your crosshairs as sharp as possible, the use an adj. obj. to focus on the target. Using the AO to focus the scope will give you problems...