The government of Brazil launched a disarmament campaign in 2004 that pays compensation to those who turn in their weapons. No questions were asked where/how they got their weapons. At one point someone handed in a high-calibre machine gun that could shoot down planes.
As a result of this campaign there have been fewer deaths as a result of gun violence. Gun deaths have fallen by more than 8% in 2004, the first time the death rate has fallen in 13 years. 443, 700 guns have been collected.