My two cents are the sighting system or uneven barrel contact with the forearm stock.
Not only can the rings be too tight, they can be both less than oval and misaligned. If you don't have the tools to verify alignment and to hone the rings for ovality maybe a piece of thin electrician tape or something equivalent may lessen a problem. That said, loose bases are the most common culprit in my mind.
The crown can be dinged like Peg said, but my focus is on the forearm/barrel contact.
Take crisp dollar and slide it down. It should not be impeded except if there is a bolt or, as in the case of a Remington, on the front pressure tab.
I have a bull barrelled Remington 700 in 308 that shot in a spiral as the barrel heated up. From 100 yards the first shot was 6-7 inches off zero at 1 o'clock spiraling in to 3 o'clock 5 inches off 2nd shot then 3rd shot 4" down at 6 O'Clock, and so on 4 more shots until shot 8 or so was in the zero position. You could let the barrel cool and if you timed the shots in the same manner it more or less exactly reproduced the same "group cluster". In afterthought that reproduction of exact grouping patterns for multiple shots should have also been a tip off that I had a shooter lying in wait.
I used a crisp dollar that would slide in the open space between barrel and stock behind the front pressure pad and moved the dollar up and down the barrel and found a few places where the wood was contacting the barrel. Anywhere the dollar was impeded or actually stopped I removed stock material. A dremel tool moved the offending wood out of the way (remember to take time to water seal a wood stock under the barrel) and left the front pressure pad alone. It shoots an honest-to-goodness nickel sized group at 200 yards now...it was a used gun I picked up at Lash's some years ago. Someone let a truly great shooter get away cheap. I still need to put a trigger job on it.
So...if you've tried everything else then take a trick from Remington and put some shims on the front forearm to put a slight, even and constant upward pressure on the barrel. I know of that fixing a couple of long guns.
Trigger pull too. Hadn't mentioned that. Anything over about 3 lbs degrades accuracy for me. At 6-1/2 lbs plus, for me, just forget it 2" groups at 100 yard regardles of everything else.