I have never shot black powder in a 38. I have shot BP in a 30-30 and reloaded with "normal" gun powder afterwards. I did tumble the cases before reloading. I found no ill effects with the reloads. I did "tap" the cases to get any excess residue out and brushed the inside of the necks before reloading. I like to economize as much as anyone (waste not, want not). On the other hand - I do not know how long you have stored your cases, if you think it has caused any corrosion to the case, I would just throw them away and start over. You are talking less than $60 for new cases and primers, a small price to pay for piece of mind. Good Shooting and Good Luck.