Why horizontal stringing? 30-06 with high BC bullets

[clearwater]

A load that previously was giving nice 3 shot sub moa groups. Some sub 1/2".
This time I got an 1 1/2"+ horizontal string and much higher and varied velocities.

The variables
1. This time tried magnum primers
2. set my bipod on a slick piece of fabric like my benchrest online friend recommended
3. had a 5 mile per hour side wind


previous velocities with winchester primers were 2600 fps
This time they climbed almost 200 fps!
Didn't even try the 1/2 grain greater load

Can a five mile an hour wind move a bullet that much in 100 yards?
Am I so over pressure I am getting wild variations in velocity? Brass, primers and extraction all seemed normal.
Is a slick fabric under the sticky rubber bipod caps a good idea?

 

[SJB358]

Something is out of wack. nearly 2800 with SB6.5 is getting up there.

Yeah a 5 mph breeze can for sure move a 2MOA load that much at 100 yards.

 

[Firebird24]

I’m going to disagree. 212 gr eld x should not shift in 5mph wind at only 100 yards. The biggest flag I see is that you are using new brass rather than once fired. I do prefer a solid rest and never use a bipod for load work up-

 

[Ralt71]

What's on the end of the barrel of this rifle?

A 200+ grain .308 bullet should not move that much in 100 yard with only 5mph wind.

Your speeds seem really fast for a 30-06 with this size bullet in it as well.

 

[Bruce Mc]

I'm guessing it's the magnum primers and the increased velocity they created.

 

[RL338]

5 mph wind should show less than 1/2” at 100yds.
A bi-pod that’s not being preloaded on a slippery surface is not ideal for load development.
Anytime a variable is introduced into a load , I start from scratch.
2 years ago I picked up some CCI 250s and they were a pain when used in my 338WM.