It's never going to be en masse. Australia enacted sufficient gun control to drastically limit mass shootings by introducing licensing, purpose and registration requirements as well as banning semi-automatics. There was a buyback scheme which most people complied with.

I do wonder if American resistance to sensible gun control will cause a flip straight over into hard restrictions, but it's difficult to see what the trigger event for that would be. Left-wing paramilitaries? (right-wing paramilitaries are seemingly tolerated!)