Zeroing at 900 ft above sea level / hunting at 7000 ft above sea level

[Greendog22250]

I am going Antelope hunting next fall and need some help figuring out my zero in relation to the altitude change. Past experience has shown me a 200 yd zero at 900 ft elev. is not even close at 7000 ft elev.
How do I compensate for this without re setting my zero when I get to my hunting location?

 

[effendude]

I have always found my short range zero remains the same, regardless of elevation. Without a verification shot or two at long range at the new elevation, all you could do is run both your elevations through a ballistics program and compare the differences. What you should see is a slight difference in the bullets path as the distance increases. My guess is that the bullet paths will remain within a moa (Minute of Antelope) for 4-500 yards easily.
Scott

 

[Chuckhunter]

What caliber, bullet make, bullet weight, and velocity are you shooting?

 

[Jet]

Just went through similar scenario on a WY antelope hunt. Used 200yd zero on my rifle fired at 500' elevation. Shot an antelope at 420yds at 7,800' elevation. POI will be different but not so much to move you out of the goats boiler room.

Like said above, run data through a balistic program (Horndy's below) and you will get an idea of the difference.

http://www.hornady.com/ballistics-resource/ballistics-calculator

You will find the thinner air will effect you more than it will effect your rifle.

Good Shooting.

Rich

 

[Greendog22250]

I am using a .308 with a 150 gr Sierra spitzer boatail Gameking at 2900 fps.

 

[Jet]

Two of the guys I hunted with used 308s (not sure of bullet weight) and they had no issues with noticable change in POI. They both hit their goats with the first shot right where they wanted it to go.

Good Shooting.

Rich

 

[Chuckhunter]

Ballistic explorer gives me these values, with a 150 Gr. Sierra@2900fps. M.V.

900ft 200yd=0, 300yd=-7.56, 400yd=-22.14, 500yd=-45.22, 600yd=-78.66, 700yd=-124.79
800yd=-186.55, 900yd=-267.44, 1000yd=-371.51

7000ft., 200yd=0, 300yd=-7.05, 400yd=-20.38, 500yd=-40.97, 600yd=-70.01, 700yd=-108.95, 800yd=-159.51, 900yd=-223.76, 1000yd=-304.15

This is the bullets path at each elevation, I can give you your click adjustments for each range at the higher elevation if you would like them. Just PM,me and let me know the scopes click values, ie: 1/8min,1/4min, etc.

 

[CharlieNC]

While the elevation change may not impact the short-range zero significantly (according to ballistics software) there are more reasons to check and verify after traveling. I use 200yd zero for hunting and make a similar altitude change, and have always required a zero adjustment of 1-3". Don't know why but that's my experience. I think temperature is one reason, as major changes affect the ammo and muzzle velocity; in addition I always keep rifle and ammo outside rather than inside (warm) at night for consistency. No reason not to confirm zero before hunting.

 

[bheadboy]

Sierra Infini 6 has an adjustment for altitude, humidity, temp and of course wind.

in a change from Ga 900ft el to Wy 4500ft elevation, lower humidity, cooler air, the drop, drift were both affected.

don't just look at the drop change as longer shots drift will also be different, as will the effect of mirage in the thiner air

Bob

 

[Chuckhunter]

After re examining the question, I believe there may be other problems. You say your 200yd zero @900 ft isn't close @ 7000ft. according to several ballistics programs there shouldn't be more than 1/8" difference between the two altitudes. So perhaps the gun or scope had been jarred during transportation. I hunted Elk at 10,000ft and the difference in my 300yd sight-in, shooting 180 Partitions@ 3066fps was 1click or.250" Check and make sure everything is tight, also do a box test with your scope, something may be amiss.

 

[Greendog22250]

Thanks guys,
When I go to WY, usually a couple of times a year, to shoot PDs, I fly. Now the bag smashers might be rough on my equipment or it is something else, I do not know. My experience,s have been more like CharlieNC - 1-3" change in elevation. Usually I am high and have to bring the scope down some.

 

[TheOtherZilla]

Why not check your zero when you get to elevation?

 

[spencerhenry]

i live at 8400 feet and i hunt up to 12,500. the lowest i hunt is around 5000. i have used the handloads.com ballistic calculator and when i input for my elevation, and temperature, there is a significant difference at ranges over 350 yards. inches at the longer ranges

if you are zeroing at 900ft and then going to 7000 feet, your zero is most likely not at 200 anymore. it might be at 210, or 215. that will make anything further seem even farther off. air density at 900 is far different than at 7000.

 

[FeMan]

I live at sea level and hunt at 10,000 ft. The affect of altitude on zero depends on the distance I zero at (100, 200, 300 etc.) and the BC of the bullet. I have found the field zero change to be 15 yards tops and less if the zero distance is small or the bullet BC higher (like VLDs).

 

[DocUSMCRetired]

If you would like you can try our software. Simpy adjust the environment section to meet where you are now, and where you plan to be.

http://appliedballisticsllc.com/ballistics/

 

[warbird2006]

I'd just try to get a bit closer to the Antelope.

Hunting is different then bench rest or F-Class. Excitement, adrenalin, friggin' cold and wind............................

 

[msalm]

Strelok or Shooter app ballistic programs have a 'zero' conditions function and a trajectory conditions function allowing you to figure out exactly what you want to know. Strelok may be the better of the two for that but it's been awhile....

 

[300 RUM]

I live at sea level and hunt at 10,000 ft. The affect of altitude on zero depends on the distance I zero at (100, 200, 300 etc.) and the BC of the bullet. I have found the field zero change to be 15 yards tops and less if the zero distance is small or the bullet BC higher (like VLDs).

Why does the AB app not work?

When you enter a zero range of lets say 1000 yards with a station pressure of 29.2 and then go to the calculator screen and enter a 1000 yard shoot with a station pressure of 23.6 you get nil for ups or downs?

 

[FeMan]

Why does the AB app not work?

When you enter a zero range of lets say 1000 yards with a station pressure of 29.2 and then go to the calculator screen and enter a 1000 yard shoot with a station pressure of 23.6 you get nil for ups or downs?

Although the AB software may give you the output you state, you know from instinct it is not correct. The 23.6 100 yard shot will impact considerably higher. Your actual "zero" distance is therefore actually farther out.

When you set up your AB software, one of the inputs is your zero distance. If you zero at say 300 yards at sea level, when you get to 10000 feet, your actual zero will be about 315 yards due to lower air density and higher retained velocity. What I do is bump the zero in my AB software when I hunt high elevation to compensate for this. The software then does everything else correctly.

 

[TheOtherZilla]

Maybe I missed it but why not verify zero upon arrival at the Antelope area?? Especially after a long trip..

Where is this hunt taking place?