Coopers are becoming more numerous the last couple decades with the resurgence of wines and spirits made in the old world tradition but they are still not plentiful or cheap! They need to make a living too.
Oh, did you mean "copper"? A copper washer is a metal washer. When you say "metal washer" do you mean ferrous? Because that's saying what you mean.
There is no problem using ferrous metals to conduct current but it would be good if it were plated or galvanized so it had some corrosion resistance.
