The city of Chicago plans to offer residents $100 prepaid MasterCard gift cards in exchange for guns, officials announced this week. Residents who bring in replicas of guns, BB guns and air rifles will receive $10 prepaid MasterCards. The city plans to exchange the cards for guns Saturday at 25 churches in its fourth campaign to collect firearms since 2006. Last summer, Chicago collected 6,700 guns. The mayor's press office did not return a call for comment. Others cities also have exchanged gift cards for guns. In December, San Francisco offered $100 grocery gift cards for rifles or shotguns, $150 cards for pistols or revolvers, and $200 gift cards for assault rifles (CardLine 12/3).