I shoot a Knight Disc Extreme in 50 cal. I began having this problem right after I bought it and found this out and from trying it works. This person shoots for Knight Muzzleloader Team.

1. After EVERY shot, run a mildly damp patch 1 time down barrel and
out.
2. Then run a dry patch 1 time down barrel and out. No more,no less.
3. My groups cut to less than half, have never had this problem again.

I shoot 100 grains 777 loose, Horn. SST 250grn.
And yes, dump the powder. I keep mine no longer than 2 years. No matter who made it or what type for muzzleloaders.