I really hate to bring this up, but "no mass shootings" does not equal "no mass deaths". There have been plenty of attacks in Europe to great effect without guns being used -- for example, the truck attack in Nice, Paris is still unrivaled by any gun massacre in America.
We shouldn't play semantic games / statistical filtering games with phrases like "reducing gun violence" and "reducing mass shootings"; I think we all can agree that our collective goal as decent human beings is work towards reducing violence/harm/death, period. Why qualify it on only gun attacks -- other than for political reasons?
If banning guns indeed reduces mass killings overall (again, it's rather a red herring to say your only goal is to reduce mass shootings rather than mass killings in general), then by all means let's work towards that.
But the data so obviously shows this to be a false correlation: Right now Europe is if anything the poster-child of why gun control doesn't work, with all the truck and bomb attacks. Again, I hate to bring this up, but so often Europeans use this as a common insult to Americans but I see this as a rather strong case of cognitive dissonance.