Re-zeroing at altitude

[jamiebolseth]

And I just uninstalled AB and reinstalled it. Now it works as expected.

Juat have to load data for about a dozen guns and loads over again...

 

[scdogman]

With a 100 yard zero this no difference. Use a ballistic app. enter zero at 100 yards and run the numbers. Keep the same zeroing data but change your current altitude to 8000 ft and see the suggested hold. Your gun can shoot the difference,

100 yard zero has benefits when dialing.

 

[Hespco]

I live at 7630' elevation & have my own range. Drop tables listed in the loading manuals are for sea level. I get much less drop than the tables indicate. For instance my 264 mag with 140gr gr bullets @ 3150 fps. For the particular BC of my bullet sighted at +1.3" @ 100yd it is suppose to be dead on @ 200. Actually is dead on at about 260yd. Drop suppose to be -31" @ 500yd. On my 522yd target it is dropping 3 to 4" less. Elevation makes a difference for drop & time of flight.

 

[Coyote_Hunter]

My process is to build a load at each 0.5g powder increment, from my starting to my top load. I shoot them, record the velocities and POIs, then look for a good 3-4 shot group. Then I pick a powder charge from the group, build several and see how they shoot.

This method has save me countless time and $$$ as it almost always results in very acceptable loads. If I was strictly target shooting I'd investigate further - but for hunting it hasn't ben necessary. Groups under MOA are common and if I gan[t get that with decent velocity I just try a different powder.

 

[hunter67wa]

I zero then confirm data with corrections at LR either MV or BC which ever a person likes. I run density altitude on all solutions. Depending on the weather at the range which is 3900' my DA will be over 6000. I went to the left coast for a class couple weeks ago with 308 calculated DA and had first round hits out to 625. I came back to WY and put a first round hit on a goat at 423 with DA inputted.

 

[skipglo]

Download STRELOK....free for Androids ..7.00 for iPhone....great simple app. That said...the difference from 1000-8000 isn't worth worrying about for GAME!

 

[BrianID]

I doubt your zero at 1000 ft elevation vs 8000 ft elevation is going to be significantly different for 100 yards. If your 100 yard zero for 1000 ft elevation is between "clicks" then I think you are over analyzing the situation to set your zero 1/2 a "click" low. That is what we like to do though and I would be setting the zero at 1/2 click low for 100 yards at 1000 feet elevation just like you are thinking about.

A 1/4" differences in zero will not make any significant difference on your hunt. What could make a significant difference on your hunt is what your bullet drop is at 500 yards. Computer programs are not going to consistently calculate this correctly. I've seen them close but you really need to test out your gun and your load at different elevations and ranges to verify the the computer data. If you plan on taking longer shots on your hunt you really owe it to the animal and yourself to test the drop.

 

[Steve Sheasly]

I've got a question/topic that I'd like to get people's thoughts on...

I live at about 1000 ft. above sea level (ASL). I hunt at 8000 ft. above sea level (ASL). I zero all my rifles at 100 yds, and dial elevation corrections in MOA for shots longer than 100 yds. Specific rifle I'm talking about is a super accurate 7SAUM shooting 175 bergers @2770 fps. I'm using the Applied Ballistics app for ballistics solutions.

The question is whether my 100 yd zero will change from 1000 ft. ASL to 8000 ft. ASL? Common sense tells me it has to. Bullet is hitting more air molecules during the first hundred yds of flight when flying through denser air, so it has to slow more. And the software computes a velocity of about 35 fps slower at 100 yds when shooting through the denser air, so that seems to back up my theory. The question is whether it's noticeable enough to even observe based on this rifle's (and my ability) to shoot roughly 0.2-0.3 MOA groups.

When I look at the AB software there's an option to turn on "Enable Zero Atmosphere", which seems like the feature that I'm looking for. To me it seems like I would enter my zero conditions at the 1000 ft. ASL environment. And then when I travel to 8000 ft I would expect the software to account for the fact that my zero conditions are significantly different. For example, I expected to see a small correction of, say, D0.25 at 100 yds when I shoot at 8000 ft ASL since the bullet is traveling through less dense air. But this is not what I see. Instead I always just get 0.0 correction for 100 yds.

Then I thought, well, 100 yds just isn't far enough to see the difference (bullets still flying to fast/flat to notice). So I set my zero distance in the computer to 1500 yds. With "Enable Zero Atmosphere" turned on. I calculated a solution for 1500 yds with the exact same conditions as my zero atmosphere (1000 ft. ASL). Not surprisingly, I got a correction of 0.0 at 1500 yds. Then I changed the conditions of the shot to be at 8000 ft. ASL thinking I'd see a correction needed at 1500 yds to account for the difference in air density. BUT - I still got a correction of 0.0 to hit at 1500 yds.

I either don't understand what the "Enable Zero Atmosphere" feature does. Or it doesn't work. Or I am just confused all together.

All this started because my perfect 100 yd zero is "between clicks" on the hundred yd target at 1000 ASL, and I got to wondering if it made sense to zero slightly low based on the fact that I would be hunting at higher elevation. So I set out to prove that my thinking was correct with the software, but I can't make sense of what I'm seeing.

Can anybody enlighten me?

Just curious where do you hunt at 8k above sea level?

 

[Greyfox]

For the past 8 seasons I have zeroed my rifle at 300Ft and temps in the 50-70F range. My hunting locations are at 3000 and 6000 feet with temperatures in 0-70F range. While I have always checked my zero upon arrival, I have rarely had the need to adjust my zero. When I did it was at most a click...and did it with some reluctance. My shots at game which have ranged from 150-1188 yards have been on target using my ballistic RF(Gunwerks G7). It does not have a program provision for a "zero" atmosphere. My recently acquired TerrapinX/Kestral 5700 outputs the same ballistic outputs as the G7. It also does not provide a zero atmosphere provision. Given this experience, If I was off during a zero check, I would more likely expect an equipment, or shooting error on my part then an issue due to atmospherics.

 

[lyotehunter]

I have some rifles that I zeroed when it was 80deg.at 4240 feet some were when it was cold. i put that in my program A.B. that stays always then when I go hunting I enter all conditions there into the program [baro,temp,wind speed,distance]. the program then gives the solution. if I can I shoot to make sure I am still on. if I am high or low I can then simply adj. my speed to put me right on target.

 

[TBell]

I've got a question/topic that I'd like to get people's thoughts on...

I live at about 1000 ft. above sea level (ASL). I hunt at 8000 ft. above sea level (ASL). I zero all my rifles at 100 yds, and dial elevation corrections in MOA for shots longer than 100 yds. Specific rifle I'm talking about is a super accurate 7SAUM shooting 175 bergers @2770 fps. I'm using the Applied Ballistics app for ballistics solutions.

The question is whether my 100 yd zero will change from 1000 ft. ASL to 8000 ft. ASL? Common sense tells me it has to. Bullet is hitting more air molecules during the first hundred yds of flight when flying through denser air, so it has to slow more. And the software computes a velocity of about 35 fps slower at 100 yds when shooting through the denser air, so that seems to back up my theory. The question is whether it's noticeable enough to even observe based on this rifle's (and my ability) to shoot roughly 0.2-0.3 MOA groups.

When I look at the AB software there's an option to turn on "Enable Zero Atmosphere", which seems like the feature that I'm looking for. To me it seems like I would enter my zero conditions at the 1000 ft. ASL environment. And then when I travel to 8000 ft I would expect the software to account for the fact that my zero conditions are significantly different. For example, I expected to see a small correction of, say, D0.25 at 100 yds when I shoot at 8000 ft ASL since the bullet is traveling through less dense air. But this is not what I see. Instead I always just get 0.0 correction for 100 yds.

Then I thought, well, 100 yds just isn't far enough to see the difference (bullets still flying to fast/flat to notice). So I set my zero distance in the computer to 1500 yds. With "Enable Zero Atmosphere" turned on. I calculated a solution for 1500 yds with the exact same conditions as my zero atmosphere (1000 ft. ASL). Not surprisingly, I got a correction of 0.0 at 1500 yds. Then I changed the conditions of the shot to be at 8000 ft. ASL thinking I'd see a correction needed at 1500 yds to account for the difference in air density. BUT - I still got a correction of 0.0 to hit at 1500 yds.

I either don't understand what the "Enable Zero Atmosphere" feature does. Or it doesn't work. Or I am just confused all together.

All this started because my perfect 100 yd zero is "between clicks" on the hundred yd target at 1000 ASL, and I got to wondering if it made sense to zero slightly low based on the fact that I would be hunting at higher elevation. So I set out to prove that my thinking was correct with the software, but I can't make sense of what I'm seeing.

Can anybody enlighten me?

down load "Ballistic AE". App and it will do it all for you

 

[CoachChris]

Just in case this comes up
"The density of air decreases with height. There are two reasons: at higher altitudes, there is less air pushing down from above, and gravity is weaker farther from Earth's center. So at higher altitudes, air molecules can spread out more, and air density decreases"
https://www.ck12.org/earth-science/...Pressure-and-Density-of-the-Atmosphere-MS-ES/

 

[Warbird2006]

I've got a question/topic that I'd like to get people's thoughts on...

I live at about 1000 ft. above sea level (ASL). I hunt at 8000 ft. above sea level (ASL). I zero all my rifles at 100 yds, and dial elevation corrections in MOA for shots longer than 100 yds. Specific rifle I'm talking about is a super accurate 7SAUM shooting 175 bergers @2770 fps. I'm using the Applied Ballistics app for ballistics solutions.

The question is whether my 100 yd zero will change from 1000 ft. ASL to 8000 ft. ASL? Common sense tells me it has to. Bullet is hitting more air molecules during the first hundred yds of flight when flying through denser air, so it has to slow more. And the software computes a velocity of about 35 fps slower at 100 yds when shooting through the denser air, so that seems to back up my theory. The question is whether it's noticeable enough to even observe based on this rifle's (and my ability) to shoot roughly 0.2-0.3 MOA groups.

When I look at the AB software there's an option to turn on "Enable Zero Atmosphere", which seems like the feature that I'm looking for. To me it seems like I would enter my zero conditions at the 1000 ft. ASL environment. And then when I travel to 8000 ft I would expect the software to account for the fact that my zero conditions are significantly different. For example, I expected to see a small correction of, say, D0.25 at 100 yds when I shoot at 8000 ft ASL since the bullet is traveling through less dense air. But this is not what I see. Instead I always just get 0.0 correction for 100 yds.

Then I thought, well, 100 yds just isn't far enough to see the difference (bullets still flying to fast/flat to notice). So I set my zero distance in the computer to 1500 yds. With "Enable Zero Atmosphere" turned on. I calculated a solution for 1500 yds with the exact same conditions as my zero atmosphere (1000 ft. ASL). Not surprisingly, I got a correction of 0.0 at 1500 yds. Then I changed the conditions of the shot to be at 8000 ft. ASL thinking I'd see a correction needed at 1500 yds to account for the difference in air density. BUT - I still got a correction of 0.0 to hit at 1500 yds.

I either don't understand what the "Enable Zero Atmosphere" feature does. Or it doesn't work. Or I am just confused all together.

All this started because my perfect 100 yd zero is "between clicks" on the hundred yd target at 1000 ASL, and I got to wondering if it made sense to zero slightly low based on the fact that I would be hunting at higher elevation. So I set out to prove that my thinking was correct with the software, but I can't make sense of what I'm seeing.

Can anybody enlighten me?

You have to re-zero your rifle (always) at 8,000 feet and then go by your software.

 

[Doug Herold]

Part of the value of setting your scope at a 100 yd zero is to be able to check whether the scope was "bumped" out of zero during transit. As previously stated, if you are zeroed at sea level, you will hold that same zero at 10k feet. HOWEVER, you will have to re-zero your rifle at distance. If you expect your longest shot (for example) to be at 500 yds at an elevation of 8k feet, you need to find a rock at that distance, shoot. and adjust your turret accordingly. This is due to the time of flight at that longer distance in less-dense air. Your ballistic app will get you close, but only live fire will confirm your zero at distance for a new location.