I only have a story for you:
About 35+ years ago, I built a 338/378KT on a Ruger #1. The cartridge had traditional shoulders and ballistics were going to be great.
Upon completion of the metal work by the gunsmith, I shot it with 200 gr Hornady's, 210 Partitions, 250 Sierra, 300 grain Barnes and about every third shot would keyhole into the target. The rifle didn't have a muzzle brake and it kicked the livin' chit out of me! On top of that it was totally inaccurate, adding insult to injury. Something was wrong and I didn't know enough at the time to fix it and I'm not sure to this day what the issue was. Needless to say, the rifle went to someone else for a different build.
I'm sure that doesn't help but it seemed like you needed a story.
Zeke