Zero for big elevation change

Discussion in 'Long Range Hunting & Shooting' started by buster2765, Mar 13, 2019.


Help Support Long Range Hunting by donating:


  1. duckhunter175

    duckhunter175 Well-Known Member

    Messages:
    338
    Joined:
    Mar 4, 2015
    I travel from Texas to hunt out west. The two biggest variables in the equation will be the air density for lack of a better term (altitude) and the temperature. They work in opposing ways and often cancel each other out or make the change so small it isn't a factor until you cross 500+.

    Example- I do my load development and zero during the summer in Texas- Temps when I'm shooting in the early AM are often 80+ (less dense air) and I'm at less than 1000ft MSL (more dense). When I hunt in OCT/NOV out west it is often much colder (more dense air) but I'm at higher altitude (less dense air). So they often come close to cancelling each other out.

    So- I will sight in my rifle with a no BS 250 yard zero and record the exact conditions in Texas. Then I go to my ballistic app and I change my temp and altitude to my expected hunting conditions and I measure the differences between my drop charts for each. I often find there is very little difference between the two at the ranges I am comfortable shooting at a game animal (500<).

    I still confirm my 250 yard zero upon arrival at my hunting destination and then I plug in my current conditions and recheck my drop charts.

    Hope this helps!
     
  2. jd126

    jd126 Member

    Messages:
    21
    Joined:
    Jan 4, 2019
    I use the same app. I tried messing with that feature before I went to Colorado but couldn't get it to output anything different. I would change the elevation from 100ft to 9,000ft but the app would give me the same ballistics. I was apparently doing something wrong. Have you tested that feature and if so, how accurate was it? The rest of the app has been spot on for me.
     
  3. Hoppsing55

    Hoppsing55 Member

    Messages:
    17
    Joined:
    Jul 11, 2015
    For example: Assuming a 200 yd zero with a 168gr .461 bc projectile leaving the muzzle at 2550fps, the drop differential at 500 yds / 4000 ft of elevation vs 8000 ft of elevation = 2.7". You may have time to check over multiple dope sheets,,, and maybe not,,, but I wouldn't want to burden myself with that mental exercise when the shot opportunity presents itself, for 1.35". You might consider keeping it simple and picking a mid range (6000ft) dope sheet calc and keep more focus on making the shot. Your ballistic's, rifle - setup, wind,,,, and other variables will all come into play. JMHO.
     
    duckhunter175 likes this.
  4. bkondeff

    bkondeff Well-Known Member

    Messages:
    346
    Joined:
    Feb 2, 2008
    First, if you have well developed ballistic data for your guns that you can currently calculate and dial, you have a good start. If you have verified that your dopes are accurate to distance where you are then the transition to WY atmosphere should be relatively simple if you stay in ranges mentioned. I feel 500-800 yds is quite manageable with decent tech if winds cooperate, in real field conditions. I hunt Idaho and move from 9500’ to 4000’ from early to late with no adjustments to scope.

    I do NOT recommend 300 yd zero. 200 keeps you always well in kill zone, and quick shots make little sense with LR equip.

    If you have enough adj capability to allow for 100yd zero, fine. 100 or 200 matters not, as long as you have field verified drop data. This is very easy in Idaho. Nice rocky hillsides with faces 300-800yd spacing, a good LRF, good spotter, and phone skope.

    Now I recommend field verifying you drops at 500-600 when you arrive at your hunting grounds. Make necessary drop adj there but not at zero. Zero adj simply for elevation will be min, but at longer distances can be enough in field conditions to concern you.

    I shoot 168gr .284 at ~2000. Moving from 0’ to 9000’ is almost 2moa shift at 750yds, while at my zero(200yd) only .3. That’s 15” vs .6”.

    So set up your system to dial, and field verify. Keep fresh batteries in your kestrel. Only use charts if your tech fails. Use charts for mid of likely hunt range.

    Dial, breath, squeeze....
     
    sika64 likes this.
  5. buster2765

    buster2765 Member

    Messages:
    9
    Joined:
    Jan 21, 2013
    I would like to validate my chart dope on sight, but don't want to be that guy making a bunch of noise a couple days before opening day.
     
    duckhunter175 likes this.
  6. snox801

    snox801 Well-Known Member

    Messages:
    2,131
    Joined:
    Sep 19, 2012
    Well to start we know that when you say long range and from Michigan you mean you once shot 250 yards. Lol
    I zero mine here in Michigan at 100 and then just let my applied app make the changes needed for my elevation. Has worked well for me. As other said usually at 100 yards it won’t matter. Because the app will ajust the rest.
     
    cschol likes this.
  7. duckhunter175

    duckhunter175 Well-Known Member

    Messages:
    338
    Joined:
    Mar 4, 2015
    I always google local rifle ranges in vicinity of where I’m hunting and I stop on my way in.

    Otherwise I find some BLM away from my primary area and set up a small target to confirm.


     
  8. jebel

    jebel Well-Known Member

    Messages:
    134
    Joined:
    Jun 15, 2018
    Yes, I've tested the Ballistics AE app several times by adjusting "current conditions" when I reach a hunt location and I've found it to be accurate. A few things that might help you get it to work:
    1. Just entering feet of elevation into the "current conditions" won't work. The program runs off of air pressure and temperature, so you need to enter those (you can leave the elevation figure blank).
    2. For air pressure, make sure you're entering absolute pressure, a.k.a. station pressure, and not the adjusted barometric pressure you get from the nightly news. For example, if you're up at 9,000 feet, the station/absolute pressure should be around 21 inches Hg.
    3. I would recommend tuning the program to your actual turret adjustments. Just because your scope turret says that each click is 0.25 MOA at 100 yards, does not mean it actually is. If you run an elevation tracking test and come out with something slightly different, you can set the app to that refined setting and it will tell you adjustments that are accurate to your actual scope.
    You can test this sitting at home. Check your trajectory at your home elevation. Then input "current conditions" air pressure and temperature for a different location. If you don't have them handy, use International Standard Atmosphere figures for both (you can find a table through Internet searches). Re-calculate your trajectory and you should see that change.

    Last, Ballistics AE is just one of several apps that do this. I'm sure there are some threads around here talking about the relative merits of one app over another, but there are several good ones.
     
    cschol likes this.
  9. Bill Peet

    Bill Peet New Member

    Messages:
    3
    Joined:
    Jan 24, 2019
    Yes , had to think about it but have read that because the air density is much thinner at higher elevation a bullet moves through it easer/ less drag . Just didn't expect it to be this much. Talked to some other people who experienced the same thing.
     
  10. Greyfox

    Greyfox Well-Known Member

    Messages:
    4,700
    Joined:
    Jan 21, 2008
    It does seem very high. A change between 600 and 7000FT requires a ballistic correction out at 500 yards of of only 2.5” with a .310BC bullet traveling at 2980FPS....5x the distance. I wonder if something else is causing such a large change.
     
  11. jebel

    jebel Well-Known Member

    Messages:
    134
    Joined:
    Jun 15, 2018
    To be clear, I understand you to mean 2.5 MOA at 500 yards; i.e., over 12” at 500. That’s significant at 500, though I agree with your point that 5” change in zero at 100 yards must be caused by more than atmospheric conditions.
     
  12. Greyfox

    Greyfox Well-Known Member

    Messages:
    4,700
    Joined:
    Jan 21, 2008
    No, 2.5 inches, not 2.5MOA at 500 Yards. The dialed elevation correction(with a 200 yard zero) at 600 ft is 6.5 MOA. At 7000Ft is 6.0MOA.
     
    jebel likes this.
  13. dfanonymous

    dfanonymous Well-Known Member

    Messages:
    531
    Joined:
    Jul 16, 2016

    A 100 yard zero, maybe even preferred is fine unless you rely on the point blank range.

    You shouldn’t need to make charts unless you are like me and don’t rely 100% on electronics but your kestrels ballistic software should recognize the change in zero from a new density altitude anyways. Meaning you shouldn’t have to rezero. The rest of your drop and wind is just a matter of how legit you trued and plug in information.
     
  14. jebel

    jebel Well-Known Member

    Messages:
    134
    Joined:
    Jun 15, 2018
    That is a mighty flat shooting deer rifle. Impressive!
     
    Greyfox likes this.