Okay, I'm thinking about trying tumbling cartridge brass with steel pins. I understand that it's done in a liquid medium so makes sense that a lapidary-type drum tumbler is required. Is there a formula for figuring out how many pounds of pins to buy for a given tumbler capacity? What kind of liquid is used, just water? How much can I expect to pay for a basic but not too small outfit? I'm not keen on doing this for small batches, like 50 at a time. Any other tips? Thanks.