Home Forums Hunting & Shooting Elk Hunting Rifle zero change at higher altitude

Going from 200 ft above sea level to 10,000 feet. Is there any way to predict the affect the altitude change will have on my rifles point of impact? 325 wsm 200gn .450 BC 2800 FPS

This will be a DIY Pulic land elk hunt. Is it ok to stop on any area of public national forrest land and shoot my rifle to check zero?

yes, go here:
www.handloads.com/calc
You can monkey with the elevation

there are calculators to help figure it out, but it would be irresponsible to NOT check your zero after a trip up the mtn. just don't do it opening morning and be sure of your backstop. you will shoot better if you know your gun does what you want vs guessing. it should not end up being enough to worry about unless you are already way high, but you really need to do it to reconfirm your zero range.

Another consideration is a big change in temps.

I live at 1500 feet. We hunt at 11,000 feet. Higher altitude makes mine shoot high so I have to lower my scope 5 clicks (1.25 moa) when we head to the mountains. I shoot a Sako finnlight and use federal premium 300 win mags in 180 grain barnes TSX.

My heavy barrel Sendero which shoots hornady heavy mags (300 win mag also) seems to not have any deviation because of altitude changes.

I have no explanation, but the point is that you best confirm your zero when you first get there. Just find a safe spot and do it. We always show up at least two days early to zero and hike in.

Altitude density, the combination of actual altitude and temperature is the best predictor of impact. Also using a 100yard zero will allow you to have fewer environmental errors when using your comeups for corrections.

Also realize this only comes into play at longer ranges with most cartridges. I hunt from sea level to 8000ft and temperatures from 40degs to 100+, until you get past 400 yards the differences are there but most cannot account for them shooting under field conditions. I do tailor cards for the expected conditions but its more about being a little OCD on it than necessary. Scounting is also a good time to let a shot or two go to check impacts well before the season.

As an example using my .270 and the 110TTSX at 3350fp:
1000ft and 90degrees my 600yard drop is -57.5" or -9.2moa
8000ft and 40degrees 600yard drop is -52.8 or 8.4moa

At 400yard there is less than an inch of difference.

All of the above..plus many over shoot because they over estimate the distance the`re shooting...a good LRF will help. Don`t leave home without one..

Yes. About any ballistics software out there will give you the answer. Makes about 1 inch of difference at 400 yards for a few of my loads.

Feel free to shoot away in our forest. Just pick up ones target when done.

Bryant
I live in North Alabama at 750ft and every time I go west to hunt I experience a change in my impact. Of course everyone knows it will vary from rifle to rifle based on ballistic data but so far here's what I have experienced with the 7mm rem mag and 257 wby. Each time I have experienced my bullet being three inches left and four inches higher at 200yd zero. Elevation has varied from 7,000 to 12,00 ft above sea level. Everyone I have traveled and hunted with out west that has been from my area experiences the same change in impact. I can say that on every hunt we have take out west we all have shot a rifle's chambered in the same caliber incase someone has a problem with ammo or a rifle. That way everyone is familiar with that calibers basic preformance and if you have to shoot someone elses gun you are that much more familiar with its limitations and capabilities. Are you hunting Colorado?

Yes we will be hunting Colorado

Why would elevation change make it shoot three inches to the left?

I was thinking the same thing - maybe that has more to do with temp's and bb harmonics???

Tx,
It seems there are variables that don't make sense sometimes but the best advice is as some have posted to check zero where you are hunting. Temperature can have a pretty profound effect as well. Altitude and air density (adjusted altitude) can be at longer distances something that has to be considered.
Something that has not been mentioned and is always a consideration at higher altitudes is the shot angle consideration. When we are shooting @ 600" Above Sea Level which is the "adjusted altitude" here in WV on the Ohio River shot angle is not usually a big deal.
Out West on top of a mountain @ 11,000' shooting downhill at a 30 degree angle @ 400 yards measured with a rangefinde with no compensation for angle feature if not compensated for will cause a miss. I think in some cases some do not give as much consideration here as is warranted.
Practice, practice, practice before a man heads out. When you get there early shoot @ 100 and 200 yards and check point of impact. Baggage handlers and riding in 3/4 ton trucks for 1600 miles seems to have some pretty drastic effects on POI sometimes too.
As for the windage difference discussed I have no explaination. Cover that issue with the POI check upon arriving.


Dave

I generally hunt elk in Colorado at 10,500 to 12,000 ft though most recently in northern BC at ??? ft. While doing so I have lived in the Bay Area of Californa, West Texas, the Gulf Coast Texas, SE Kansas and Calgary, Alberta. I have never tweaked my sights after zeroing them where I lived and have had zero problems with deer or elk out to ~300 yards. My ability to shoot dictates whether I hit or not so I don't worry about altitude.

Bryant: I used to live at/near sea level and sight in my Rifles at the S.P.A.A. range in Seattle, Washington at an elevation of 25' above sea level!
Then I would drive over and Hunt Wyoming, Montana and Utah at elevations up to 8,500'!
I know first hand the differences in trajectories at differing altitudes.
Yes varying altitudes not only changes your sight-in point of impact, but the higher you go the flatter your bullet will fly (out past your original sight-in point)!
A person needs be aware of these things and adjust accordingly.
A projectile intended for one particular point of impact at sea level IS going to be off at 10,000' and said projectile will fly flatter out past the original sight-in distance.
Go to a ballistic program and obtain the trajectory chart for your particular bullet/loading at sea level then compare it to one you will make for 10,000' in elevation.
I now live and do a lot of Hunting right at 6,000' in elevation and I understand the atmosphere to be only 85% as "dense" here at 6,000' as it is at sea level - that illustrates what your bullet is dealing with (going through?).
One of my neighbors and gun trading buddies retired 3 years ago and moved from sea level in Northern California to 6,000' elevation - he had to start using oxygen soon after he moved here.
He just returned from his first prolonged visit back to sea level where he was able to get by without an oxygen assist at all!
When he got back home to SW Montana here and had to start toting his oxygen bottles with him again!
Best of luck there in the high country this fall and learn about and watch out for "altitude sickness" before your Hunt.
I have seen altitude sickness develop at 7,500' in folks from low country - it's painful and debilitating while one is under the influence of altitude sickness.
Hold into the wind
VarmintGuy

Don't forget to let your rifle and optics adjust to prevailing conditions (especially the temperature). This is where you may see a drift over several days in the wood of your rifles (so oil them prior to your just before leaving site in). It is very dry here. And drink lots of water.