some bores have a might tighter tolerance , and as such, some don't like certian sabot/bullet combo's
and this is also why many muzzleloader company's make what they call EASY slide sabots and even bullets to help loading in very tight bores!
this is also why many modern inline users also have gone to cleaner burning powders, like blackhorn 209 and such
they also sell cleaner firing primers too
all the little things can help make life easier
you'd be surprised how dirty a fired primer can make a bore pending brand of primer
so, my suggestion is maybe to try some different sabots/bullet combo's
many love them powerbelt for how easy they load?
in very tight bores they tend to shoot pretty well too , or in my experience they have!
although I never really hunted with them, found other combo's my guns liked better, but they have grouped well in many inlines I have shot!
and I am not pushing any brand here either, just giving you options to maybe make loading easier for you