Is it possible to identify which banks do business with gun manufacturers/dealers (for boycott purposes)?

If the gun manufacturers are publicly listed companies, their banks would be identified in their quarterly or annual reports. However, in most cases, if they are not publicly listed, you will not be getting this information. The gun manufacturers are a small part of the equation. There is a complete allied industry around gun making that together encompasses what one would call the gun manufacturers.

Pretty much these companies would deal with the Top 25 or Top 50 banks in the US. Boycotting them would not be an answer. Gun manufacturers also might consume McDonalds. Boycotting that won’t also do any good. The root problems need to be identified (and in most cases have been) and you need to take action on that.