Imr 4831 has worked best for me with 90-100 grain bullets in the 243 Winchester. H4831sc and H4350 has worked well in most I’ve tried also, but I got better performance with imr 4831in my rifles.
I just read your post about eliminating the primer as culprit. If you haven’t tried loading cartridges one at a time I would try just to make sure bullets aren’t getting reseated under recoil. The other thing I would try would be to remove the muzzle break if you can and try without it. I’ve had...