A huge SO WHAT? So the theory is that someone hell bent on murder, the worst possible thing a human can do to another human, will go to a gun shop to buy the ONLY TOOL he could possibly use to MURDER?
See the problem to start with?
Somebody hell bent on murder is likely going to achieve it one way or another. In other cases you might have somebody going through an emotional episode. Could be a domestic altercation, could be a firing from the work place, maybe a spouse was found cheating, or their dog just died who knows. But if a person is in an emotional state and wants to inflict harm on themself or another then a gun is the most efficient and destructive tool to use so doing something to prevent emotional purchases could prevent death. It doesnāt necessarily have to be a waiting period, thatās just one idea. The point is to do our best to make sure people who buy and own weapons are responsible, law abiding citizens and of sound mind. Can we at least agree on that last point?
Sure, we should try to stop felons and the mentally ill from getting guns. and we already have all the processes in place to do this, no new ones are needed. What do we need? We need the police to follow through and actually apply the ones we already have.
We do not need to limit access to guns by law abiding people based on the extremely rare mass public shooting. In fact, the thing driving these mass public shootings are the democrat gun free zones we have created which make sure that those emotionally disturbed people you mention, have an easy, unarmed target.
Since all research shows that armed responses to mass shooters drives them away and stops them when they happen, we should focus on getting rid of democrat gun free zones.
And to this point...nothing proposed achieves what you want. Not raising the age to buy rifles, magazine limits or waiting periods.