I posted this a couple of years ago, but I really I lucked out once. This kid inherited a bunch of guns from his dad (about 700 of them, including some NFA items). His dad had a whole bunch of BP replicas and had fired all of them once and put them in a safe, uncleaned.
I cleaned the bores with hot water, then plugged the nipples/flash holes and soaked the bores with Evapo-rust overnight and they came out perfect.
I got a '52 Springfield musket rifle with bayonet for $150, a '51 Mississippi rifle in .54 caliber for $150, a Pedersoli Harper's Ferry pistol for $100, and a Dragoon Pistol Carbine for $125. I'll kick myself for the rest of my life for not getting the Pedersoli Brown Bess with a bayonet. It was originally $250, but he marked it down to $150. On a later trip to the store, the owner sold me an assortment of roundballs (.57, .53,.73,.68) and two dozen .69 minie balls for $20. The guy took one out of each package, shot it, and put the gun and it's balls away.