Altitude effect

[Cactus5479]

I am headed west to shoot (at) prairie dogs. I expect all of my shots will be 500 yds or less. My .22-250 is zeroed at 250 yds at 400 ft above sea level. However I will be shooting at the little varmints at slightly over 4,000 ft above sea level. How much is that going to affect my zero and trajectory out to 500 yds, assuming environmental factors are equal? I plan to check my zero again when I arrive.

 

[sixfivefanboy]

with a 250 yard zero it will have an impact, you shots will be high - with a 100 yard zero it won't altitude won't effect your zero. you should be able to plug it into an ballistics app and figure it out.

 

[Quintus]

Do you have another gun or two you can bring as well? Good towns make hot barrels fast.

 

[Mikecr]

You didn't reveal your internal ballistics, so nobody could guess about actual zero change.
Your intent to re-zero, removes the need to know what zero change would be.
Trajectory would be be predicted with any program for this, still with 250yd zero, and expected hunting conditions.

 

[waveslayer]

Zero at 100 yards, download a good ballistics app and you are in business. All my rifles are zeroed at 100 yards, even my ELR stuff.

For good ballistics apps, Trasol and Applied Ballistics are my go to's.

 

[sixfivefanboy]

I am headed west to shoot (at) prairie dogs. I expect all of my shots will be 500 yds or less. My .22-250 is zeroed at 250 yds at 400 ft above sea level. However I will be shooting at the little varmints at slightly over 4,000 ft above sea level. How much is that going to affect my zero and trajectory out to 500 yds, assuming environmental factors are equal? I plan to check my zero again when I arrive.

Zero at 100 yards, download a good ballistics app and you are in business. All my rifles are zeroed at 100 yards, even my ELR stuff.

For good ballistics apps, Trasol and Applied Ballistics are my go to's.

There is really no reason not to zero at 100 yards if you are spinning elevation turrets. When I am out hiking around looking for deer or elk, or out coyote hunting I just dial my elevation up for MPBR. if it is outside of MPBR I dial more elevation. I guess if you don't spin turrets and are using hold overs, a farther zero might be necessary.

 

[Bob2650]

I have had a curious experience with altitude and NRA Bullseye Pistol competition. My home range was just east of Denver at about 5,100 feet elevation. When I went to Gunnision, the range is at something like 8,000 feet, I had to adjust the sights UP a couple clicks on the 22 pistol. It was a Hammerli 208s with ultradot scope. My 45ACP seemed to hold zero with the elevation change. I am a High Master 2650 club shooter so 2 clicks out of zero is very obvious to me at 50 yards. This is counter-intuitive and I never figured out how this could be.
A: why the 22 and not the 45?
B: Why is it backward? The 22 shoots low at high altitude.
Bob Fleming

 

[arch408]

A ballistic program like Strelock should give you all the information you need. But IMO, the wind will have more effect on the bullet then the altitude difference.

 

[BallisticsGuy]

With most high power rifles shooting high BC bullets the difference is close to nothing to 500. After 500 differences start getting big enough to notice. For all of my rifles the difference is ~.1mil (~.36moa) at 500. If you give us your velocity and BC and scope height we can give you a more precise answer but honestly inside 500yrds, don't trip unless your BC is really poor or velocities unusually low by high power rifle standards.

 

[waveslayer]

I have had a curious experience with altitude and NRA Bullseye Pistol competition. My home range was just east of Denver at about 5,100 feet elevation. When I went to Gunnision, the range is at something like 8,000 feet, I had to adjust the sights UP a couple clicks on the 22 pistol. It was a Hammerli 208s with ultradot scope. My 45ACP seemed to hold zero with the elevation change. I am a High Master 2650 club shooter so 2 clicks out of zero is very obvious to me at 50 yards. This is counter-intuitive and I never figured out how this could be.
A: why the 22 and not the 45?
B: Why is it backward? The 22 shoots low at high altitude.
Bob Fleming

What's the temp stability of your powder for the 45?

OP. Spend the money on a ballistics app since you are already spending the money coming out here to slay some prairie dogs

 

[Bob2650]

That was many years ago, now I live in Texas.
I use VV N310 for my 50 yard target loads in the 1911. Frame mounted scope.
I did not notice a temperature issue but there are so many things critical to rifle reloading that make no difference in the 45ACP that I am not supprised. If I would let the ammo sit in the sun a few hours I have no doubt I would see higher velocity but the target ammo is loaded so far below max it would still be considered wimpy. The exception being hardball 45 ammo which I load to full military spec just to mess with the softball 9mm shooters and the fact that my 1911 hardball pistol likes it full power for the best accuracy.

 

[User4302021]

I have had a curious experience with altitude and NRA Bullseye Pistol competition. My home range was just east of Denver at about 5,100 feet elevation. When I went to Gunnision, the range is at something like 8,000 feet, I had to adjust the sights UP a couple clicks on the 22 pistol. It was a Hammerli 208s with ultradot scope. My 45ACP seemed to hold zero with the elevation change. I am a High Master 2650 club shooter so 2 clicks out of zero is very obvious to me at 50 yards. This is counter-intuitive and I never figured out how this could be.
A: why the 22 and not the 45?
B: Why is it backward? The 22 shoots low at high altitude.
Bob Fleming

Because your .22 was zero'd for 50 yards. 50 yards is first incidence for that setup. This is the first time the bullet crosses line of sight on it's way up.

Therefore, if your round is shooting flatter (such as the high altitude you mentioned), it will shoot BELOW point of aim.

 

[Cactus5479]

All good info guys. Many thanks. I am taking multiple rifles, each of which likes a different load. I burned just under 1,000 rounds last year in 4 days but had a number of misses high at the longer ranges. One is 35.0 gr of W748 behind a Hornady 52 gr HPBTM (G1 BC 0.229), chronographed at 3558. Another is 39.0 gr of W760 pushing a 55 gr Sierra BTSP (G1 BC 0.245) at 3449. The last is 33.5 gr IMR 3031 behind a Hornady 50 gr V-max (G1 BC 0.242) at 3671. I think I will re-zero at 100 yds and run the ballistic calculations set at 4000 ft. Do you think that will keep me within minute of prairie dog at 450 or less if I'm dialing elevation turrets based on range? I will be using Nikon's stabilized rangefinder so I'm pretty confident in ranging out to those distances.

 

[Bob2650]

First, I would like to apologize for the thread drift. While this is not about rifles, it does illustrate that there is little substitute for actually testing your loads at the distances your interested in. Back then we did not have Kestrel or Applied Ballistics. We recorded data for the range card by lots of shooting. I highly recommend some kind of weather meter and a good ballistics program to help out with the range card. It do not advocate relying strictly on the electronics because just like dependence on a GPS you will be asking to get lost someday. O-crap, more thread drift! OK, Here we go:

My pistols are set up to be zeroed at 25 and 50 yards at the same time. I do not need to make any adjustments during the match. This is accomplished with selecting scope rings to put the scope at the right height on the 22 and for the 45 I shoot different loads at 25 yards and 50 yards. The 50 yard load is 4.4 grains of VV N310 under a Nosler 185 grain jacketed HP, which is selected for accuracy and the 25 yard load, 3.4 grains of Bullseye under a Star 185 grain swagged lead HP is adjusted for elevation. That is not enough power to cycle the pistol with a slide mounted scope. The 22 load is by Eley.