A lot of sound advice offered thus far. Having a rifle that will not shoot to one's reasonable expectations / performance standards is frustrating to say the least.
Now approaching 60 years of precision shooting, I've only had a few that fell into this category albeit, my standards are not at the benchrest or competitive shooting level.
Here's my checklist**
1. All screws tight and properly installed.
2. Sound bedding system.
3. Bullet matches twist rate, and Powder is suitable for caliber in question.
4. Scope ruled out as culprit.
5. Testing conducted in favorable conditions, i.e., wind and mirage minimal, moderate temperature.
6. In my experience, if you clean to bare metal using strong copper solvents, it may take several rounds to establish some bore equilibrium to produce consistent POI. The repeated use of these solvents only exacerbates the problem. The repeated stripping the copper out, re-plating the bore cycle creates an unstable bore in my experience. Using a mild solvent such a Shooter's Choice or Hoppe's 9 to remove the carbon and some copper produced more consistent results for me.
Sometimes, a rifle just won't shoot to your standards no matter which corrective measures you try. For example, I had one, a Remington 700, 22 250, Varmint model. Fought it out with Remington and they finally agreed to examine it and pay for the shipping. After they inspected the rifle, they apologized stating that the rifling was 'crosscut" whatever that means and sent me a new rifle which shot fine.
The other rifle was a Weatherby Vanguard. I spent a lot of time and money on it and was able to finally get it to shoot about 1 moa which, for my performance standards at the time, i.e. varmint hunting, was not acceptable.
At some point you have to "turn mother's picture to the wall" and move on. Life is too short to continue when you reach your limit of patience which is different for different folks.
**The reason I never buy used rifles is you have no idea what the former owner has done to and with the rifle. After what I've seen at the range over many years, my position was only reinforced many folds.