My personal suggestion would be to use loose powder. With pellets you're kind of stuck with whatever accuracy they give and there's really little room for tweaking. You can either use 3 pellets or 2. Or buy some of the lower grain pellets and try that. But with loose, you can start at a certain point and increase the charge by 5 grains to find your optimum load. It will take some time shooting 3 round groups and letting the barrel cool consistently but it will get you to the best accuracy possible for that specific bullet.