I learnt the hard with my 260rem a little while back. I had been shooting Lapua brass and it did shoot wonderfully well, however given the pain in the ass it was to neck up from 243 I switched to RP cases for a hunting trip. Turned out the new remington brass had the same bullet shooting four inches high and three inches to the right. I should've known better, I certainly do now.

I am a self confessed doofus sometimes.

Experience is something you get, just after you needed it.