This was my first outing with the rifle so the only thing I can think of is that the mag primers or the dyna tek bore coat raised pressures. Does that make any sense?
I had a .264 WM that I treated with bore cote, and I had obvious pressure signs with less than max "book" loads. Took it to a gunsmith who ran gauges down the bore and he found what he called a constriction a few inches ahead of the throat. I'm not saying that's happening with your rifle, just something to consider.
