Shooting a 22" 6.5 cr 140 amax. Have my rifle/scope zeroed at 100 with exact elevation and windage adjustments out to 1000 yards in 100 yard increments. My adjustments are based on sea level measurements and I'm going out to an altitude of 5000 ft. in a few weeks. The question is how will the 5000ft affect my adjustments, and is there a formula for this? Hope this makes sense to you all. Thanks for chiming in.
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Advanced Marksmanship Does your Zero change at different altitudes? And if so.......
- Thread starter LOCOBEAR
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I don't know the exact formula to plug in. But inputing into a ballistic calculator should show less drop and windage needed to be on target. What type of muzzle velocity are you getting with your setup? I can run it through shooter and see.
Your best bet is to run a ballistics solver. I believe the latest "guidance" is to use "station pressure" rather than density altitude but if I'm wrong on that I have no doubt I'll be swiftly corrected.
Big picture you should see less drop and less affect by the wind on your round at higher altitudes.
Big picture you should see less drop and less affect by the wind on your round at higher altitudes.
I don't believe your 100 yard zero will change (and I'll be swiftly corrected as well). That is one reason for zeroing at 100, as the atmospherics don't have "time' to act on the bullet at that distance. There was a rather lengthy and informative thread on this awhile back, but I don't recall the title.
Run the ballistic calc based on the map altitude, then re-zero at 100yd onsite. If you use your old zero all your comeups will be based on a zero that only exists at your lower altitude, and new POI will be progressively higher than calulated as distances increase.
While it may be true that density altitude will vary with barometric fluctuations, the calculated scope adjustments should get you on paper regardless. Unless you are denying yourself the option of sighters, you should be OK.
Gravity and air resistance operate on the trajectory at every instant of flight. While the differences may not be large enough to notice with the Mark I eyeball, they do exist. Otherwise, somebody has just found a way to momentarily suspend the laws of physics. They always apply. Always.
Greg
While it may be true that density altitude will vary with barometric fluctuations, the calculated scope adjustments should get you on paper regardless. Unless you are denying yourself the option of sighters, you should be OK.
Gravity and air resistance operate on the trajectory at every instant of flight. While the differences may not be large enough to notice with the Mark I eyeball, they do exist. Otherwise, somebody has just found a way to momentarily suspend the laws of physics. They always apply. Always.
Greg
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Found a Ballistics calculator on Hornady's site. I input a 10 m/h wind for both elevations. Claims are pretty much as you've all said. And from the calculations it looks like things start changing slightly at 300 and jump at 400 on.
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So what you are saying is zero will change at 5000 ft. even though calculations show they are identical? I see on the calculations the wind (set at 10 mph for both elevations) does change POI by .1 inch. Best if I re zero at 5000 ft. just to be safe. But this was very interesting. Thanks again.
In the purely academic, theoretical world, yes. Differing altitudes have different density altitudes. The greater the density altitude, the less resistance to the flight of the bullet resulting in less drop for a given distance.
But for all PRACTICAL HUNTING scenarios, not so much . . .
But for all PRACTICAL HUNTING scenarios, not so much . . .
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True, both. The difference at 1000yd with be lost in the margin of atmospheric inconsistencies between shots.
Zero doesn't change,
it's also why you can put your "Zero Conditions" and "Current Conditions" in a ballistic calculator. To adjust your dope at distance. Nothing starts to change dope wise until about 300 yards, even then it will be within the accuracy of your group I'm sure unless you are shooting sub 1/4MOA at 100.
At 100 it's inside the width of the bullet, and certainly your accuracy.
Dont sweat your zero, just adjust the conditions at distance for the shot. I zero here all the time (5000ft+) and never have an issue at sea level, just run the dope for the new conditions. Shooting Oregon my 800 yard dope here was 6.8 miles and 4500 ft less it was 7.2. As long as you know your current conditions you're fine.
it's also why you can put your "Zero Conditions" and "Current Conditions" in a ballistic calculator. To adjust your dope at distance. Nothing starts to change dope wise until about 300 yards, even then it will be within the accuracy of your group I'm sure unless you are shooting sub 1/4MOA at 100.
At 100 it's inside the width of the bullet, and certainly your accuracy.
Dont sweat your zero, just adjust the conditions at distance for the shot. I zero here all the time (5000ft+) and never have an issue at sea level, just run the dope for the new conditions. Shooting Oregon my 800 yard dope here was 6.8 miles and 4500 ft less it was 7.2. As long as you know your current conditions you're fine.
6.8 miles huh? You truly are operator as fuck. Where does one obtain a scope that tracks that far? Can I get a package deal that includes tactical thumbs?
Lowlight is correct.
I use Shooter and it has your zero conditions, then you input the current condition to offset the difference. It does work, I have had many out of state hunts using this method with great results
I use Shooter and it has your zero conditions, then you input the current condition to offset the difference. It does work, I have had many out of state hunts using this method with great results
A density altitude reading (not station pressure!) from a kestrell plus a Whiz Wheel or FDAC with your specific load (bullet, muzzle velocity, etc) will get you what you need regardless of your elevation.
Well, I guess you have go look at it from different view points.
You are zeroed at your home range. You have your "zero".
You go Yeti hunting in Nepal. Your density altitude is 21,000 feet, or some other God awful altitude. So, you run your dope.
Your shot is 2.5 miles. Normally you would have to come up "X" mils to be on target for a first shot head kill.
But since your density altitude has changed from your normal "zero" density altitude of 100 ft ASL you will take note that you don't have to dial up as much because the density altitude is much greater.
Your "zero" is the coincidence of your poa and your poi at a given range and physical conditions (humidity, altitude, temperature).
You don't change your "zero" you just change your settings for the required range based on the changes of those physical conditions from your "zero" conditions.
You are zeroed at your home range. You have your "zero".
You go Yeti hunting in Nepal. Your density altitude is 21,000 feet, or some other God awful altitude. So, you run your dope.
Your shot is 2.5 miles. Normally you would have to come up "X" mils to be on target for a first shot head kill.
But since your density altitude has changed from your normal "zero" density altitude of 100 ft ASL you will take note that you don't have to dial up as much because the density altitude is much greater.
Your "zero" is the coincidence of your poa and your poi at a given range and physical conditions (humidity, altitude, temperature).
You don't change your "zero" you just change your settings for the required range based on the changes of those physical conditions from your "zero" conditions.
Technically, no.
If your DA changes enough from where you first zero'd your weapon your POI will be higher or lower than zero depending on the change in DA. If you go back to where you zero'd your weapon and fired, your POI will be dead center whereas if you went up 6k in DA, your POI will probably be higher than your POA from your original zero.
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