Barrels, in my experience, can be individuals meaning sometimes they require different approaches.
You said you tried only removing the carbon and that "brought you only a few more rounds." Does that mean you extended the acceptable accuracy round count a few beyond 75?
In your carbon removal process, do you use a bronze brush?
In the dozen or so rifles I own, none of them respond well to harsh removal of copper. When I do that, I get first shot flyers, and require 5 to 10 rounds, depending on the rifle, to reestablish desired POI. All respond well to removing the carbon. Some require more frequent carbon removal than others. Most general solvents will remove some copper, but I found, in my rifles, that leaving some of it in place retains accuracy and most importantly, first shot POI. I know this goes against popular positions on cleaning, but I can only report what I have experienced.
I would consider a round count of 75 with acceptable accuracy acceptable. You may want to experiment cleaning every 60 rounds with a general solvent that focuses primarily on carbon like Hoppe's 9, Shooter's Choice, or Bore Tech C4. Use a bronze brush with about 15 passes, refresh the brush after 5 passes. I can PM you my procedure, it's quite simple, doesn't take a lot of time and works for me.
But as others have stated, a barrel replacement may be the prudent option given the price of components these days. Personally, I have a hard time giving up on a rifle and sometimes that drives me too far into the "rabbit hole" without acceptable results and I end up re-barrelling the rifle.
