Doomsday Gun 1994 on netflix

Dr Gerald Bull was a genius at designing and building superguns (very large long range guns capable of shooting at ranges more than 100 miles). When an operational plan by the CIA to export sanctioned arms to apartheid-South Africa through him was exposed, the CIA denied all knowledge and he went to jail. He was later released, and moved to Belgium to start a subsidiary, of which a major project was to help Saddam Hussein build a new supergun capable of firing over 500 miles.