Case over pressure and altitude.

You say you used new brass? Are you saying the new brass was shot in Louisiana? If you worked up brass to near max load with fireformed brass and now using new, or if you happen to be using brass with a different head stamp than you worked up with in Rapid City, could easily explain it. I have a hard time believing a few inches of mercury pressure change in atmospherics has enough effect on internal ballistics to push a load over the edge.

In the case of the 30-06 and the 22-250, it was the same batch of new brass.

However, you may be onto something with the -08. Looking at my records, that is a plausible explanation.
 
this sort of reminds me of something i ran into a while back with a wsm when I started turning necks and setting neck tension, same lot of brass but when I set the neck tension low like .001 my pressure seemed to spike and I got a sticky bolt and could tell the recoil was sharper on the same load I shot for a few years, when i tighten it up to .003 it settled down . only thing i could think of was it was moving to the lands at lower speed and acting like it was loaded to the lands.
 
Doubt your change in pressure has much to do with the atmospheric pressure. The round is essentially a closed system when fired and not really exposed to the pressure change, with the exception of the bullet. Would be interesting to test in a controlled environment.

Would say that new brass is the likely cause. Brass, even from the same manufacturer can vary in hardness. Ambient temperature, bore condition etc are other things to take a look at.
 
I've seen this when firing new brass then loading the fireformed brass to the same load.
I think the new brass is a little more forgiving, meaning the case expansion helps hide the pressure if you are right close to max.

Lesson I learned was the load isn't proofed unless it's shot through fireformed cases.
 
I would suggest you go back to SQUARE 1

1. Check your rifle, Copper buildup, carbon ring and such.

2. I would check powder weighing and measuring equipment for accuracy.

3. I Suggest you take 5 or 10 shells from each rifle and pull the bullets and weigh
the powder and check the powder to verify powder type.

4. Also check the new cases for fit to the rifle chamber. If some of the cases are short to shoulder for the chamber they may be getting a jumping lick at the bolt face and giving you pressure signs.

In checking the Hornady 7th edition the 22-250 Rem. max load is 36.4 (Thirty Six and Four Tenths) of Varget, your load is near 2 Gr. under Max.

Good Luck in finding the problem and be safe in the process.
 
Well.....I think I found the explanation. It is a bit embarrassing for me, but if others can learn and prevent a serious issue so be it.
I had said there wasn't any difference in the loads. That was technically correct. The loads were the same, except in the way they were measured. I just connected the dots that I used my new Chargemaster to throw the loads. I also used my phone, which contains my load data, in close proximity to the scale. As it turn out, this is a sure fire way to mess with the accuracy of the scale. I recently went back to the old 505 beam scale, and no more over pressures.
Since discovering this, I've done some research on how to get the most out the Chargemaster. An upgraded power supply, ferrite chokes, no more cell phone, and a McDonald's straw of all things really have it performing well.

Well that's enough for now. Just proving my dad right that no man is entirely useless, he can always be a bad example.
 
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