In an authoritative study, the National Academy of Sciences reported that "the theory underlying gun buy-back programs is badly flawed and the empirical evidence demonstrates the ineffectiveness of these programs."...
Imagine that instead of guns, the Oakland police decided, for whatever strange reason, to buy back sneakers. The idea of a gun buyback is to reduce the supply of guns in Oakland. Do you think that a sneaker buyback program would reduce the number of people wearing sneakers in Oakland? Of course not.
All that would happen is that people would reach into the back of their closet and sell the police a bunch of old, tired, stinky sneakers.
Gun buybacks won't reduce the number of guns in Oakland. In fact, buybacks may increase the number of guns in Oakland.
Imagine that gun dealers offered a guarantee with every gun: Whenever this gun gets old and wears down, the dealer will buy back the gun for $250.
The dealer's guarantee makes guns more valuable, so people will buy more guns.
But the story is exactly the same when it's the police offering the guarantee.
At $250 per gun, the Oakland program cost $250,000, most of which was not even budgeted. Tabarrok notes that "the first two people in line at one of the three buyback locations were gun dealers with 60 firearms packed in the trunk of their car." He wonders why police don't cut out the middlemen and buy guns directly from manufacturers.
[Thanks to Don Boudreaux for the tip.]