There’s not enough information given to pinpoint your issue...
Sounds like back in 1999 when I loaded some of Barne’s first all copper offering with blue coating and no lube grooves in my 243. It was the bullets fault. The blue Barnes were a smaller diameter than my rifles bore. I couldn’t shoot a barn if I was locked in it with those Barnes. Barnes finally realized their problem and started making their bullets larger in diameter and putting softer alloyed lube grooves in them to be able to expand when traveling along the rifling like cast dose to get acceptable accuracy with their bullets now. I’ve had the same issue with cast bullets and the wrong powder combo and or lack of neck pressure from an improper crimp. I’ve had shot strings shoot straight down when my scope slips. I’ve also had the same issue with smaller diameter Agulia bullets in my CZ452...six to nine inch groups at 25 yards.
First thing I’d tell you to do is clean, clean, and clean, your barrel...then clean it again. It could have a lot of copper or lead build up. Remove your optic. If there is a picatinny type rail bed it with acraglass or blue loc tite. My optic on my ruger American 450 bushmasters came loose and slid several times and eventually wrecked an optic, loosened my action screws, and wobbled my trigger loose trigger wrecking it as well before I figured out the never ending loosening rail vibrating everything loose on my rifle is a common issue with American’s. Oh yeah, the bolt release wore so bad the catch pin would fall out of the gun when the action was removed from the stock. I even sent it back to Ruger for the non stop loosening issue after I loc tited the base down. They removed, inspected the base, and shot it five times and retuned it. THE REAR BASE SCREW WAS FINGER LOOSE AGAIN WHEN I UNBOXED IT FROM RUGER! You would have thought they would have checked it after shooting??? Guess not, I removed it, and installed Rugers updated true picatinny rail and acraglassed it to the action along with blue loc titing the screws. I’m sure some acraglass mixed In on the screws to keep it from ever coming loose again. I explained I was testing cast bullet loads in it and maybe put 200/250 plus rounds through it. Ruger told me the Americans weren’t meant to target practice and was designed for the average shooter who only goes into the deer woods a few times and maybe shoots two boxes through it in a lifetime!...Right from the Ruger reps mouth! A price point gun that is made not to shoot...often, or it will fall apart. When you reinstall your optic I suggest to use 3m adhesive on the inside of the rings first and let it dry before installing your optic...or some rosin. Then make sure you spend the $40 and buy a wheeler torque wrench to torque your base screws, scope mount, and rings and action screws...did you check to see if your actions screws loosened? Lastly, try a box of factory ammo. I had a scale go on the blink last year and was throwing hot charges that locked my bolt in place and caused fliers.
If none of this fixed your problem you have at least ruled out 99.9% of what it could be. If non of this fixes the issue I’d have someone with a bore scope check your rifling...or lack of rifling.
With a HUGE 6” group at 25 yards IF it was your rings fault you should have been able to visually see the scope slippage or felt or see it move or rattle loose lMO. I’m sure you were using a rest for testing of some sort and not free handing when shooting your rifle weren’t you when you shot your 6” patterns?
There’s WAY more to the issue than rings to get 6” groups at 25 yards going on IMO.
Something is really loose, your barrel is shot out, improper ammo, really loose action screws, or major flinching(which I doubt happened) I would guess is the culprit.
I blamed 2 optics, three sets of leupold and warne rings, and my ammo till I found the factory picatinny scope base rear screw loose and wear marks on where it vibrated the bluing off on my receiver.
Oh, I did have one other rifle shoot just as bad. An old enfield I changed the stock on. It was wiggling around in the replacement stock as I shot giving pie plate groups at 100 yards out my lead sled. I acraglassed the complete rifle in its new stock and the same ammo I was using tightened down to .5” groups. Check your bedding as well.