I would NOT trust a coffee can to handle the weight of much lead! Get a cheap chinese cast iron dutch oven or check your thrift shop for a used one.
Nobody that casts boolits(bullets) is so tight that they can't spend $10 for a cast iron pot. Folks that are too poor to get a $10 cast iron pot could save enough money by not going to McDonalds just once, not getting those two packs of cigarettes they need so badly or saving the change from their pockets for a month or two. Better safe than sorry.