Rifle Scopes Change scope zero with altitude change

[DaveMT]

Bullets are hitting the bullseye at 200 yards at altitude of 5,500 feet. Scope elevation knob is set to zero. If I do not change the scope elevation knob; then, bullets will hit some unknown distance below the bullseye at 200 yards at altitude of 3,000 feet.

How many MOA do I need to turn the elevation knob up to hit the bullseye at 200 yards at altitude of 3,000 feet?

I am using JBMBallistics with:
“Std. Atmosphere at Altitude” IS CHECKED.
“Pressure is Corrected” is NOT CHECKED.
“Elevation Correction for Zero Range” IS CHECKED.
“Target Relative Drops” IS CHECKED.
All other options are NOT CHECKED.

I would like to sight in my rifle at a range near my home. Then I would like to avoid the hassle of sighting in my rifle again by shooting at a bullseye at 200 yards at a different location at a different altitude. My problem is that I don’t know how to get the answer to this question from JBMBallistics or from any other source.

What are your thoughts, knowledge and experience.

Dave

 

[cramey74]

I am circling the (D). D=not enough info

 

[Quickdraw40]

DA won't change a short range zero enough to worry about.

 

[Rob01]

If you are going somewhere where a shot will matter whether it be a match or a hunt then check your zero at the location you will be shooting if the opportunity is given. Not to would be stupid.

 

[sinister]

I've taken a rifle from 6500 feet to 58 feet above sea level and the variation was less than a quarter minute. Same as going from 300 to 10,000.

The differences are much more drastic the farther the bullet travels.

 

[vinsonr]

I've taken a rifle from 6500 feet to 58 feet above sea level and the variation was less than a quarter minute. Same as going from 300 to 10,000.

The differences are much more drastic the farther the bullet travels.

The differences would be the same, 1/4 MOA is 1/4 MOA no matter the range.

 

[sinister]

The difference is air density the farther the bullet travels.

Your 100 and 200 yard zero shifst will be negligible.

Your 1000 yard zero at sea level will not be the same at 10,000 feet above sea level.

 

[bohem]

I've said this a number of times, it seems to be showing up a lot more on this forum lately, but try running the numbers if you don't believe me when I say this:

The change in altitude affects the shooter FAR more than the bullet at short range zero distances and inside appx 350yd with a 308 there is no correctable offset from sea level to the top of Pike's Peak. That means that the angular shift on paper for a 100, 200 and even 300yd zero is less than the common subtension unit in our scopes. You might calculate that the shift is (for example) 0.6" at 300yd, but if you have a 1/4MOA click in your turret, how do you make that change? The 1/4 MOA turret moves the bullet a little more than 3/4"

The vast majority of the problem is the shooter, addressing that will get you far better ROI for your time than trying to figure out how to dial out the shift with a scope that isn't designed for it.

 

[DaveMT]

Cogent Answer

I understand your answer. My knowledge has been enhanced. I will no longer worry about bullet impact at the altitudes that I am likely to encounter. Many “Thanks” to all. This thread may now be terminated.

 

[Rob01]

The rifle doesn't shoot itself. Also effects on the ammo and not just external ballistics need to be accounted for. If you don't check zero if the chance presents itself then you deserve what you get. Some people have to learn the hard way.

 

[cmica]

interesting to know this. Thought it would change too.


but then again going to different zones I would target shoot anyways to make sure it's still zeroed in after travel

 

[bohem]

Spot on, Rob. Always double check when you can. My point is to remove the additional question of external ballistics being in question, they are not.

Shooter, travel bumps/dings/etc., and drastic temp changes on the powder and primer compound.

I'm far from advocating that you shouldn't recheck, instead, I'm saying to look elsewhere beyond the DA change.