I am having the same problem as you with my 50 cal.cva kodiak, so I have tried many combinations also and my cva really likes the hornady 230 grain xtp's with mmp black sabots.I can get 3/4 inch groups at 60 yds. with those and I am far from being a great shot.these are the only xtp's I have tried thus far so maybe and hopefully it will like the heavier ones also.I use both hodgdon rs and triple seven the triple seven giving me the best results at about 95 too 100 grains,the rs at 105 grains.I have tried a 214gr.cast bullet 44 cal. in a sabot with not much luck so far , I have ordered a 45 cal. Lee mould from medway and will give that a try also.I guess this is the fun of using a muzzleloader, trying all the different combinations.I have a t/c omega and it isn't half as fussy.
Good Luck,