Sodium Hydroxide will attack copper, but Ammonia will do a better and faster job: Ammonia actually forms a complex with the copper. You'll see that as the solution turns a really strong blue colour. I would avoid any chlorides. They tend to cause persistant rusting, and with acid conditions (the salts of strong acids, such as sulphuric, HCl, Nitric, and weak bases such as iron and copper are acidic. Salts of strong acids and strong bases e.g. sodium chloride are neutral, weak acids and strong bases give alkaline salts e.g. sodium or potassium carbonate) Anyway, back to acid conditions: rusting can only occur in acidic conditions, and as iron is more reactive than copper, it would be the gun which would corrode, not the copper plate. Go for ammonia Keith