You do realize that the 5 minutes is an exaggeration right? Its usually about 30-45 minutes by the time you complete the paperwork, the background check is ran by the feds. If your background check is clean, its about a 5 to 10 minute phone call. Plus, if someone walked into a gun store angry and upset, MOST gun stores are gonna turn him away as they are allowed too.
You're also talking about punishing people for the actions of 1-2 people a year. 52% of Americans have guns, with an estimated 500 million in civilian hands, if guns were the problem, you would truly know it.
Evil will find a way. Murder itself is illegal, what law do you propose to make murder even more illegal to where a murder or prospect murder stops and reconsiders their actions?