"Brown Stuff" in My Barrel

[derfhunter]

If the pitting in on the lands it will probably affect the accuracy, especially if it disrupts the sabot. The treatment you have done should smooth that out a lot.
If the pitting is down in the grooves and the sabot does not come in contact with it the barrel will probably shot pretty well. I have shot a couple muzzleloaders with pitted barrels that shot pretty well.
Like others have said the pitting makes the barrel cleaning chore a lot harder.

Good luck, Hope it shoots well for you

 

[Smyrnagc]

The pitting is on the lands and runs in circles from the breech plug area about 1/3 of the way up the barrel.

 

[Flatlander.54]

Lots of good info and advice here...the bottom line is your not gonna know until you take it out and shoot it. I have seen ML barrels ate up with pitting that shot just fine, but they were a real pain in the butt to get clean afterwards.

For future reference...anytime you buy a use ML...always pull the breech if possible and inspect the bore. Or, at least run an oil soaked patch down the bore and see what comes out. If the seller refuses this opportunity...pass on the sale cause they probably know the bore is in pitiful shape.
If you buy used online always ask for a 3 day inspection period. You would be amazed at the amount of guys out there that dont clean these guns properly and just let the bore go to ruin.