I just finished up zeroing at the range today for my upcoming pronghorn hunt in Wyoming. I'm zeroed dead nuts on at 200 yards. However, since I live at 950' above sea level, I'm wondering what will happen to my zero when I get to Wyoming where I'll be hunting between 5000' to 7000' ??? Does anyone have a ballistics program that can calculate this??
Mine will not and I don't want to have to use a lot of my 2 boxes of handloads to rezero when I get out there. More particulars on the load:.277 caliber 140gr Accubond BC of .496 , velocity of 3125 fps. The rifle is zeroed at 200 yards and 950' above sea level. Scope height is 2". I think that's all the parameters. I would really appreciate if someone can tell me how much up or down I need to move my zero to be zeroed at 200 yards at 6000' altitude. Thanks.

I have a Sierra program that will do this. If no one answers you, I'll run it for you when I get home. The BC is increased as you go highr, thinner air, so it should shoot flatter, but your 100yd zero shouldn't bet too far off (ie, if you are +2" @ 100 it will be close to that).

What will the temperature be in Wyoming compared to where you zeroed? What will the barometric pressure be. And did you forget humidity? All of these have some slight effect on your zero, just as does altitude.

Since a 200 yard zero is on the short side for pronghorns to begin with, just be happy that your rifle will be zeroed for about something more like 205-210 yards. If you can judge the difference between a pronghorn at 200 and one at 210, then you possess an outstanding and unusual talent.

Your zero is much more likely to have drifted due to conditions of the trasport of your rifle, like drying of the stock or a slight bump to the scope mounts than to have moved in any meaningful way due to the change in altituede. Always shoot your rifle after transporting it, most especially if your trip has been by common carrier.

Your zero will move up at the higher altitude because the drag on the bullet decreases (air is less dense at altitude).

It is fine to run a ballistics program to get some idea of your zero change but my strongest recommendation is to shoot your rifle again when you get out to WY to get your new zeros.

I calculated this about 15 years ago and for the elevation change from 80 feet above sea level to 4500 ft, I think the zero moved less than 0.5" at 100 yards. So, I haven't bothered with it since.

the change isn't worth the time to think aboout it unless you go 240,000 miles to the moon....then you should be concerned....here on earth...it's nothing.

You do need to test fire when you get there but I ran this through my Sierra program:
6000ft
100yds = +1.0"
200yds = 0"
300yds = -5.30"
350yds = -9.9"
400yds = -15.7"
450yds = -22.8"
10mph/9:00 wind = -10" @ 400yds
I would personnaly zero for 250 for goat hunting but you can get inside 250yds if you work hard. Any change do to elev. will show up past 300yds, even then it's less than 2" way out at 400yds.

Guys,

I zeroed that way for a reason!! I have a Burris with Ballistic Plex reticle. I verified my 300 yard mark today and also shot a 1/2" 200 yard group, deas nuts on zero. On my first elk hunt out in Az, I remember that after zeroing my .338 here, it was either low or high out there, I don't remember which. That's what I'm trying to avoid, I don't want to use up all my ammo(handloads) sighting in out there and not have enough to hunt with. fredj338 thanks, but I think you misunderstood. My ballistics program gives me that info also, what I need is the actual difference the altitude will make from my initial zero here. I suspect that it may hit higher out there but can't verify it. I don't think ballistics programs really have that capability. I use a Nikon Monarch 800 laser rangefinder to take the guesswork out of the equation. I'm just trying to be as prepared as I can be since the outfitter said that the shots will be on the long side of 300 yards.

First , I would pack along more than 2 boxes of loads on such a trip . Sure , one or 2 shots is all you will need to take the goat , but it's best to be prepared for Mr. Murphy , and a guy can use alot of ammo rezeroing a rifle or scope gone wakcy , or (hopefully not) chasing down a cripple . Or ,you may decide to shoot a few varmints .

Secondly , it would seem to me to you would want to verify your zero after arival in any event , especially if you figure the shots are likely to run on the long side of 300 .

bowhun, it's not really a problem:
@ 1000ft:
100 = +1.02"
200 = 0
300 = -5.62"
@ 6000ft:
100 = +0.98"
200 = 0
300 = 5.39"
So if you are 1" high, on @ 200, you are still 1" high on @ 200. Any diff. will be minimal, something like a 205yd zero. Have a good hunt, I'm off for Montana for goats as well.

You're rifle will shoot high at those higher elevations, so it's strongly recommended that you fire a few test shots at 200 yds to see just how high and lower it a bit when u get there. I'd guess 2" or so difference in point of impact at 200 yards at the elevation you're talking about and depending on temps too.

I once overshot a mule deer with my .308 M70 due to this factor. I'd sighted the rifle at 200 yards at about 1200' elevation and trained extensively with it all summer for the hunting season. When I went to the Flat Tops Wilderness area of western Colorado our hunting camp was at 10,000+ feet.

I took the shot from a treestand at about 175 yards and he dropped as if struck by lightning. When I got over to him I realized I'd pulverized his spine right at the withers - a very effective shot but NOT where I'd aimed... I'd held at about midchest in line with the shoulders. Later on I was reading Elmer Keith's book on big game rifles and saw a paragraph where he had learned this same lesson and nearly overshot a deer due to significant elevation changes from where he'd originally sighted in. Of course if I'd read Elmer more carefully before the trip I'd have known that he already told us about this phenomenon over 50 years earlier!

Well, I have some land in Colorado at 7800 feet. Going from Phoenix to this land doesn't really impact my 200 yard zero, but it is a few inches at 400 and a hell of a lot at 700.

So anyone who says it doesn't matter really hasn't tried it.

BTW, when you use ballistics programs, be sure to look at total drop, as most will simply "readjust" your specified zero, making it appear that the result is inconsequential.

As AnotherAZWriter mentions there are noticable effects once the distance increases, and probably so for the more rainbow like trajectory cartridges/bullets.

Several years back I did a comparison test out to 700 yards with a 300 Win mag. I had my data from ~600 ASL (home data) and compared it to on-site data at ~10,000 ASL (hunting area). Once I re-zeroed (100 yard zero) on-site I ran a trajectory comparison between the known ~600 ASL and the ~10,00 ASL. My trajectories compared within inches on target until I reached 500 yards. At 500 yards I noticed that I needed about 1 MOA less elevation at 10,000 ASL as compared to 600 ASL. This ~1 MOA per 100 yard difference continued to accumulate so I ended up with 2 MOA less elevation required at 600 yards, 3 MOA less elevation @ 700 yards, etc, etc... My 10,000 ASL 900 yard data was ~19 MOA total for the 180 Nosler BallisticTip at 3100fps muzzle.

My data is always based off a 100 yard zero and testing at intervals (typically 100 yards). When I arrive at a new hunting site I always check the rifle zero and reset if if needed then verify ballistic trajectories to the anticipated hunting distances.

ASL - (Above Sea Level)