It made a difference in the U.K. and Australia didn’t it?
The problem might be the US is too far gone but not being able to walk into a shop and just buy a gun would definitely lower shootings.
The people doing mass shootings aren’t career criminals who’d buy a guns off the black market they’re mentally ill people who’ve just grabbed it out of their parents closet.
A country with poor care of mental health + legal purchase of guns = lots of mass shootings.