In the movie Lord of War starring Nicholas Cage, they bought 3,000 real guns for the film because it was cheaper to buy real guns and sell them back later than buying prop guns. They also rented 50 tanks which were to be sold to Libya a few months later. – WTF Fun Facts
Source: Why ‘Lord Of War’ Starring Nicolas Cage Bought 3,000 Real Guns Instead Of Props – CINEMABLEND