A few hundred times, did you alternate arms? A BP workout!Some good suggestions so far. I'll just add my 2 cents in dealing with a rusty .50 cal. bore on an old traditions deerhunter a friend inherited. I plugged the nipple and filled the bore with PB Blaster. I left it overnight and was able to remove the nipple and bolster screw with difficulty. I wrapped a piece the green scotchbrite pad around an undersized brush and brushed the bore a few hundred times. It took out the rust, some pitting was left and the gun tested out to be a good shooter all things considered. About a 2 1/2" group at 50 yards. I was careful with the Blaster but did not notice any damage to the blueing.
I have an odd 13 gauge ML BP shotgun, a tight 12…Damascus stubb, fluted barrels, possibly Scandinavian, I had to remove 150 years of ‘crud”… Scotchbrite, 0000 wire wool, and Kroil helped…
It’s rough, but goes bang when needed.
Cheers!
Steve1