Rich,
Just to clear up your post, Aqua Fortis is not nitric acid, it is made from nitric acid. You mix the acid in about 3 or 4 parts water then add iron until it won't dissolve anymore. Lots easier, safer and cheaper to just buy it. Easy to find, any muzzleloader supply store has it. I don't have too much confidence in the vineger, some swear by it, just my opinion.
Bill