Try NOT "fouling", loading into a clean dry barrl, and then dry-patch your barrel.
The fouling from just buring powder in your barrel would be different than the powder burning under pressure of a load I would guess...maybe not.
I seem to be seeing a pattern, or a regular repeat of people having these problems, who are all using Bore-Butter.
I may be wrong...just seems like that.
I always hunt with clean guns, don't snap caps or flash the pan. I do carefully dry all critical parts of the gun with clean, dry patches, bore, breech, pan and frizzen, and on a cap gun take the nipple out, dry it, dry the flash channel, etc...and they shoot to POA first shot. I've always been highly "dubious" of fouling a rifle before shooting it. Seems like pre-fouling a rifle also would make it more prone to attracting moisture and maybe getting mis-fires.
I've used a variety of patch lubes...concoctions of bacon grease, olive oil and bee's wax, Hoppe's #9+, Wonder Lube 1000, and other stuff.
Again, first shot from a cold clean barrel will be right in the kill zone.
Are your shots going into a kill-zone sized area, for the maximum range you hunt, and appropriate size for the animal? Or are you getting too hung up on group size?
Put up two paper plates at your self imposed maximum range, and shoot one shot at one from a cold clean barrel, and a follow up shot at the other one. Hit the plates both times? If so you are ready to hunt. You won't be shooting for group on the side of a deer or elk.
Just some thoughts.
Rat