Vertical Dispersion and a Tail Wind?

mmattockx

mmattockx

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Yesterday I was out doing some final load development work for this fall's hunting. Conditions were not great, with a gusty, turbulent quartering tail wind running around 20kmh. The wind was coming across the side berm of the rifle range, giving a noticeable vertical component to the gusts.

I was working on my 6.5x55 and had a load that twice previously had shown very little vertical dispersion, but this time it had a bunch. Charge weight was +/-48.0gr, with a 140gr SST, range was 200yds, MV should be around 2700fps, maybe a bit higher.

Could this much wind cause 1"-2" extra vertical at a relatively short range like 200yds? Groups were not terrible at 2"-3" (under calm conditions they were around 1.25"-1.5"), but the vertical sure bothered me because none had previously been shown.

Mark
 
Yes. turbulence can push you around alot.

remember that the wind is likely swirling and tumbling as it goes over the berm - think surf crashing on the beach.

It can bounce you around alot.

20km winds is a very strong wind and has to be accounted for.

Test on a day with lighter winds or in a direction that doesn't go over land obstructions.

Tailwinds tend to push your shots up. Headwinds tend to make you shoot low.
Jerry
 
Mission has a range that has some pretty funky 300 yard verticals. Wind from the left causes updrafts and winds from the right cause down drafts. The mother of all up and down ranges is Homestead in Alberta. Most definitely nose and tail winds affect verticals, and you can even plot that in many ballistics programs. Getting the wind to stay consistent...priceless.

Find a condition and stick with it, or load develop in dead calm... and only hunt in calm weather :)
 
Obtunded said:
Find a condition and stick with it, or load develop in dead calm... and only hunt in calm weather :)
Click to expand...

Isn't that the truth? I wouldn't have chosen those conditions, but it was when I could get out and the conditions at home were much better than when I got to the range. If it had been blowing like that at home, I wouldn't have bothered leaving.

I was reasonably pleased at the groups I got, considering the conditions, but it didn't help that much in choosing the load I will use on deer in a few weeks. I am close enough that it really won't matter, but I like to have it really pinpointed if I can. Ah well, next time.

Thanks for the advice, gentlemen.

Mark
 
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