There are too many good bullets around to mess with something that defies logic.
I have been using `154gn Hornady's for years to form cases for a 280AI simply because it and my other 7mm rifles either side of that velocity range, will not shoot them well. This points a finger at the bullet more than the rifles in this particular case, with this particular batch of bullets.
When you have a rifle that shoots sub MOA with some reliability, it makes it harder to accept a 2+ inch group from the same rifle. Some times it is bullet defects such as weight variation, caliber variation or being under sized for the caliber, internal issues or what ever. Powder variation less so as I have seen bench rest shooters tweak powder charges using a powder thrower at the bench not bothering to record the charge until they find one they like. The accuracy levels they seek are beyond usual factory rifles and shooter ability, indicating that to some degree, powder charge variation is not the primary culprit.
Now, changing a primer can make a difference. Not every time and not with every bullet and cartridge combo, but often enough to take it seriously. I often change primers when developing loads to determine favoritism from the rifle.
