evidence: Waiting periods saved 750 lives per year in the 17 states that had such policies in 2014, according to the study Handgun Waiting Periods Reduce Gun Deaths, which was published in the Proceedings of the National Academy of Sciences. [...] A gun waiting period, typically between two and seven days, acts as a "cooling off" period, preventing would-be gun owners from making spur-of-the-moment purchases that could fuel violent outbursts. Delaying the acquisition of a gun might also close the window of opportunity for a perpetrator to use the weapon, if the only intention for making the purchase was to do harm within a certain period of time. [...] While the call for waiting periods is bound to receive some pushback, the researchers are encouraged by the broad support waiting periods receive. The American Medical Association supports waiting periods for gun purchases, and polls show that a majority of Americans—and even a majority of gun owners—back them as well, the paper says.