Tailwind affect advice

[Windtech1]

Today I was flummoxed by a strong -- 15MPH -- dead straight tailwind.

Shooting a 338 Lapua Mag I was accurate to my 500 yd zero nearly every shot.

However, when I walked back just 250 yds to 750 I lost my bullet.

I'd hold high, low, left and right but never hit a 2'x2' target.

Rifle is accurate.

WInd was moving across flat prairie fields with seemingly no influence.

But, I'm thinking there is some weird affects.

I'm hoping for some insight from others.

By the way:
2800 estimated velocity
500ys zero
750ys -- plus 7.5 moa (shooting into 10mph headwind)
1000 yds should be plus 16.33 moa but I have not yet verified with actual shot.
Berger 300 OTM
89gr Retumbo

Thanks for any info.

 

[FearNoWind]

A "dead straigt tail wind" or compartive head wind should have zero value. But that assumes the terrain is perfectly flat with no undulations to generate eddies and that the wind direction didn't change at some point down range. Sometimes, a wind that feels "dead straight" from the front or rear is actually somewhere in the area of 10:15 to 1:45 or 12:15 to 1:45 o"clock and that would create a half value condition. Factor in about half an inch of spin drift at 700 yards and you've got some calculating to do.
Are you using verfiable BC figures in your ballistics calculations or the manufacturer's claimed BC?

 

[Windtech1]

After sleeping on it and taking another look at the 500 yd hits I think you are correct about how I might have misjudged what I thought was a full value 6 oclock wind. I was pushing my bullet left by 1.25 moa @500 and still never really moved the impact -- it suggests I was pushing into more of a cross wind than I thought. Also, I'm using the Berger ballistic program data. So far, in my limited attempts at 1000 yds I have found by changing velocities until two bullet drops that match up to the data I can find what I think is a good velocity number -- Again, in my limited attempts it is giving me repeatable MOA settings. Thanks for the thoughts.

 

[Windtech1]

Also, I am wondering if headwinds are more stable to shoot into than a tailwind?

 

[FearNoWind]

Also, I am wondering if headwinds are more stable to shoot into than a tailwind?

I find tailwinds more difficult to judge than headwinds. Probably my own idiosyncrasy because, technically, there shouldn't be any difference. Even so, depending on the terrain, a tailwind bothers me more than headwind and that sometimes influences me to make an unwise adjustment in lining up the shot. We all have bad habits to work on - I'm no different.
Wind is as fickle as a high school cheerleader on a blind date. It need not be the shooter's nemesis - we have to work with it and not fight it. So I make every effort to remain in the realm of average wind velocities and average wind direction at the muzzle for making wind calls while giving consideration to flag averages (if flags are available) over the target distance.