Something that may help. I bought a mint .250 Ruger Model 77 from a person I did not know but he seemed trustworthy. It wouldn't group four inches at 100 yards. I was more disappointed in the young man than the rifle. I tried a dozen different combinations of powder and bullet with little improvement.

Live and learn. Out of the blue months later, driving home in my half-ton , I remembered a gunwriter somewhere describing the importance of tightening the bolt that angles up under the magazine cover. Bingo! The kid who thought he was unloading a palooka sold me a MOA tackdriver.