Happy Hunter, are right in your statement to work up to a max load!
In your case, I think that the lot# of powder that you currently have is probably 5-10% hotter than the lot# that they used in establishing a Max load for the book, which is another reason to use some common sense in approaching Max loads.
Reloading manuals are just an indication of what a maximum load is in the worst cases whether it be -125* or +125*, minus what the lawyers think is a margin of error to protect them in a lawsuit.
No doubt, that you may have a bore that is undersize that may lead to much higher pressures which would also be evidenced by more copper fouling.
What happened to you does not happen that often, but it does happen, none the less!
If 8208 is Varget, I ran into the same problem with my previous 22/250, with higher pressures than what the book indicated was Max...I realize that the book is only a guide. The reloading manual can not tell me what is a Max load for my rifle, only I can.
I have seen instances where the lot# of powder is 9.0g off on what is a max load for my rifle because that particular lot # is VERY slow as seen by shooting across an OHler 35P
Chronograph.
It seems to bear witness that the slower the burning rate of the powder, the greater the potential for a margin of error in what is a max load for your rifle.