After 100 shots with sabot loads, I wouldthink it would be time to give the bore a thorough scrubbing with something capable of removing plastic deposits. Try 90 grains loose FFg T7 and save some money. Work your charge upward in small increments until you reach a point where accuracy goes south. I'm not much for sabots but plain ol' Hornady XTPs in correctly fit sabots are not only much cheaper than the pre-packaged stuff, you can try several different sabots to find the one that loads easiest while still producing good accuracy.

Another think you might check is the fit of the metal to the stock. It should be nice and even with no points exhibiting more pressure than others. Small tweaks can make large differences so change only one variable at a time before testing.

ChrisW noted that rifles have individual tastes so don't expect your buddy's load to work best for you (even though it might).