Research coming out of the Johns Hopkins Bloomberg School of Public Health has found that regulating guns sales can actually reduce lethal violence. Common sense policies like restricting firearm access for perpetrators of domestic violence and felons reduce violence. People opposed to gun control in the US like to argue that there are already some many guns out there that regulation won't reduce crime rates. Here's evidence against that point.
A review of 28 published studies examining U.S. gun policy found that laws and regulations designed to keep firearms from people at risk of committing violence, such as felons and those under restraining orders, are effective and, in some instances, reduce lethal violence. The researchers also found that certain laws, including rigorous permit-to-purchase laws which require a permit to be issued before completing a handgun sale and comprehensive background checks, are associated with keeping guns out of the hands of criminals.