new here, but have had similar problems with new guns - Rem. 700 Mountain 280 Rem, and Tikka T-3 in 7MM Mag.
I switched brass, primers, bullets, and everything else you can think of, and then took a look at the barrel/stock bedding. Found high spot/twist in stock on Rem, and not the best bedding on the Tikka.
some work with sandpaper/dowel fixed the Rem., and judicious filing/sanding of the bedding block in the Tikka solved the problems.
Found the Rem, due to slim barrel contour only likes Sierra 160 SBT's, while the Tikka will print sub-MOA out to 400 yds with anything Flat Base between 120 and 150 grains. Nothing over.
Just may experiences.