Hmmm... A heavy lead oxide coating that is very hard. Might they be recoveries from a CW 'digger,' because it sounds like they have been in the ground for a pretty long time. Take them out of the water, let them dry and put them in little window boxes on cotton. They sell well at CW shows, local museums and on occasion even eBay. Honestly, the variations in the different types and manufacturers of Minnies is a study unto itself. Diggers around here find discarded (dropped by CW soldiers who didn't want to carry them) Minnies by the jars full, all the time and they look just like yours, as described. If they don't have any more historical value, to you, than old lead water pipes, by all means throw them in you casting pot and recycle (don't you just love using those 'green' terms) them into RB of your choice (another word that celebrates our diversity- I'm on a roll here!) Good luck!