After shooting some cast bullet loads, etc that I can easily clean the bore down to bare metal as viewed with a bore scope with some Ed's Red and ten brush strokes or leave it alone and continue to get good accuracy.
Other loads produce a hard black fouling that can be felt resisting the first patch and is very hard to remove. If the bore isn't cleaned accuracy is degraded. In the bore scope it looks like a black varnish,with some fraction of bare metal depending on how many cycles of bore cleaner and brush have been applied It seems to be worse with some powders than others. It happens with rough bore as well as very smooth ones.
ER, Butch's Bore Shine, or Kroil doesn't seem to touch it. JB and a lot of elbow grease will eventually work. I tried Slip 2000 which is supposed to dissolve the carbon on gas piston parts in 15 minutes it is also supposed to be non toxic, non flammable, non hazardous, biodegradable and even smells nice -- but it doesn't do a thing for the black fouling.
The bore looks OK by eye after normal cleaning and I would like to ignore it but anything that makes it very hard for the first patch to pass can't be doing cast bullets any good.
Any suggestions to either the cause or the remedy?
John