It just won't shoot like it used to, no matter what ammunition or scope I use.
I think I was over zealous cleaning it. Damaged the crown or even the bore.
There are several reasons why a rifle will suddenly stop shooting well, and you've touched on a couple of them. If your scope and action screws are tight, and the scope tracks and holds zero when mounted on another rifle, its no longer part of the equation.
If you haven't cleaned with a powerful copper cutting chemical, you could have a buildup of copper in the bore. If you do use a powerful copper cutter and have cleaned down to bare metal, you might have to put 50 rounds through the bore before it begins to shoot well again. If you use ammonia, or a solvent with a high ammonia content to clean the bore, be sure all of the ammonia is removed and is not allowed to evaporate while in the bore, as this is the action that causes corrosion, and pitting. Its true that improper use of a cleaning rod can damage a bore, but it would mean you were extremely careless allowing the rod to repeatedly slap the bore walls, you didn't use a bore guide, or perhaps you used a stainless brush in a stainless barrel. The condition of the barrel can be assessed by a gunsmith with a bore scope, and he can make recommendations from what he sees.
If the barrel has seen lots of shooting, the chamber throat could be badly eroded, but this can be mitigated before replacing the barrel; by choosing bullets with a long bearing surface, by seating your bullets long, and/or by having a gunsmith shorten the barrel shank and re-chamber the barrel, or by simply rechambering to a longer cartridge, say from .243 to 6mm-06, if your action is long enough to accommodate the longer cartridge.
If the bedding surface between a wood stock and the action has softened due to exposure to gun oils and solvents, the rifle won't shoot. Depending on the degree of contamination, it might be cured by glass bedding, or you might have to replace the stock. If the rifle fired a large number of rounds with loose stock screws, the bedding surface will be damaged, and the rifle won't shoot. Glass bedding will restore the accuracy of the rifle If you removed the pressure point from the barrel channel to attain a free floating barrel, it might have improved accuracy, it might have reduced accuracy but improved consistency (no fliers), or the rifle's accuracy might have taken a dump. The solution is to experiment with shims in place of the pressure point, until the sweet spot is found.
If the crown of the barrel impacted a hard object, it might have deformed, negatively affecting accuracy; cutting a new crown should resolve the issue. If there is bore damage near the muzzle, the barrel can be shortened, and a new crown cut.