Every muzzle loader I have had has been a chore to find the perfect load combo,say you take 2 knight disc 50 cal like you have,load both of them with with 100 grs or pellets and say a 250 gr. hornady bullet,451dia.and shoot both at say 50 yds neither will hit the same you might get lucky and both be quit similiar but not alike.One might have a very tight group and one may have a big group,or both might not even hit the target.
The best way I have found to find the best load is pick a bullet you want to use,go to the range and try loads say from 80 grs to where ever they start to spread out,you may have to try different types of powder even,it all depends on what size groups you are satisfied with.if nothing in that bullet works you have to go to another one and so on.
Last sumer I spent over $200 bucks trying to get a T/C encore 45 cal. to shoot groups I was satisfied with,never did find anything to shoot in it so I sent it back to T/C waiting to see what they say.
I wanted to shoot small bullets so I worked to get groups I wanted in my encore 50 cal,I didn't just drop a small bullet in and it shot one hole groups,I had to shoot and shoot till I found one that satisfied me.But with a lot of trying many different bullets ( 200 grs and less)and powders and loads till I found what I wanted.Last spring and summer I went through 2 1/2 lbs of 777.1 1/2 lb pyrodex select,2 boxes of pyrodex pellets,and 1 lb of clean shot,and I haven't even a guess to how many different bullets.
every year I see a lot of guys bring their muzzleloaders to the range and set up a target at 50 yds if they get 2 bullets to hit near the bulls eye they are accurate for them and they are ready to hunt.
I have a mk-85 I got when they first came out using a nosler 185 gr bullet and 100 grs of clean shot it will shoot as good as a reg rifle out to 100 yds.have a ruger 77/50 it will shoot very tight groups using bullets Hornady XTP from 180 to 250 gr with 100 grs of cleanshot or 100 grs of pyrodex select.The 50 cal encore shoots with a barnes 195 gr and 100 grs of pyrodex or 100 grs of pellets.
I don't know what all you have tried but if you want try 100 grs of pyrodex or 2 pellets and a 250gr or 300 gr in the barnes bullet,a lot of guns I have seen shot usually shot these with good groups.
Hope this helps.

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