Question for experienced EXBAL users

[Alan Griffith]

I've been running my EXBAL for a couple of years now and I think I may have figured something out and wanted to run it past those with lots of EXBAL expereince.

On Monday, I got a good 100 yd zero and entered in all the data into EXBAL and saved it under "Save sight in conditions".

Yesterday, I was shooting a tactical match a solid 1400 ft higher in elevation. When I got to the range, I checked my 100 zero and not thinking moved my zero up .5 MOA. During the match I used current weather data. We had a paper Osama BinLaden target @ 600 yds and my 3.5", 5-shot group was 3.8" high. I can't account for the .8" but I think the 3" high wouldn't have happened it I'd left my zero alone. Do you agree I should just have shot the match using the previous zero and left well enough alone or did I do the correct thing by adjusting my zero to the higher alt and lower Baro?

Alan

 

[Lindy]

Re: Question for experienced EXBAL users

I think you should have left your zero alone.

A 100 yard zero is virtually unaffected by the conditions in which you zeroed - unless the temperature is drastically different.

That's because 100 yards is too short a distance for changes in atmospheric drag to affect the point of impact.

Paying attention to changes in zero conditions comes into play mostly when you are using a longer range zero, especially 500 or more yards.

For example, early models of the Barrett M82 came with built-in 60 MOA bases, because the scopes of the time didn't have enough elevation to go well beyond 1000 yards from a flat or even a common 20 MOA base. So, the guns were zeroed at 500 to 1000 yards - and it's pretty obvious that atmospheric drag will change at those distances with conditions, effectively changing your zero range.

If you were going to adjust your zero with the increase in elevation, you should have moved your zero <span style="font-weight: bold">down</span>, not up, because the air is thinner.

A half MOA at 600 yards is 3.14 inches - close to the error you recorded. The remainder is probably normal variation in elevation at distance.

So, in short, if you zero at 100 yards, leave it alone.

 

[IsleofGough]

Re: Question for experienced EXBAL users

Just what Lindy said. Even if you shot at 14,000 feet, (ten times higher) your zero would only need 0.1 MOA adjustment (less than your scope probably even has)

 

[Alan Griffith]

Re: Question for experienced EXBAL users

Yeah! I thought so. At least it was easy to dial it back. Thanks,

Alan