Small powder charge gives 1/2MOA HORIZONTAL movement - wierd

[jfseaman]

I've sometimes wondered if any of you hold off for crosswind when doing load development (at 100 yards, anyway)?
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Not me. I don't care about windage but want a very consistent vertical. Of course, I try to go when it is not windy.

 

[Brians356]

Of course, I try to go when it is not windy.

That goes without saying! Unfortunately, truly windless mornings are not very common where it is legal to shoot in N. Nevada. In the high desert, nights are always cool, and as soon as the sun comes up and hits the cool ground, the convection starts stirring things up, even with snow cover. Afternoons are always windy in summer from adiabatic (downslope) winds off the mountains. Mark Twain called it the Washoe Zephyr. The best mornings, cloudy but calm, are very rare. Clouds here almost always mean there's a front coming through with wind.
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[randy x]

Try 38.5 and 38.8

 

[Tim s]

This was shot round robin on very calm conditions. With sun out and 40 degrees

This shift isn't weather

Shot off solid concrete bench
Front rest was a Seb NEO with rubber feet to eliminate slipping.
Rear bag is a Edgewood gator.
Pretty much free recoil (slightly touching shoulder to meet f-class rules) with 2 oz trigger.

Rest adjustments was never touched except via joystick.

I have good clean fore/aft movement in the bags and I'm able to hold on target about 3/8" (@300 yards)

Never adjusted scope (vortex golden eagle at 60x) after first of 3 sighters before test started.

I tried do to all rounds 50-60 seconds apart capturing velocity via lab radar and writing it down. This gives my eye some rest time and to simulate a twenty round relay.

I didn't post the 6br 2 load test that I did immediately after shooting the 6x47...
the 6br was less than 3/4 at 300yds

So I don't know what else this could be

You have two problems.
First, testing at 300 yards is less than ideal and you introduce far more variables than what you are looking for through testing.
Second, there is no such instance as no condition at 300 yards.....ever, and you're testing methodology of 50-60 second spacing, actually makes everything else mentioned, worse not better.
You would be far better off testing at 200 yd and spacing your shots in 15-20 second intervals until bbl gets warm.
There is a reason benchrest shooters try and get 5 shots down range in 30 seconds or less and has much to do with the fact that conditions rarely return to where they were, especially at 300 yards.