It really doesn't matter what other countries do, as few have the same sorts of guarantees in their founding documents. Certainly, we can learn from some other nations, but the lessons aren't likely to lead where you seem to want to go.
I believe we agree on the problem (too many gun deaths,) but your apparent solution simply isn't plausible. We haven't see anything like the massive swell of support it would take to alter the 2nd amendment. Any policy change likely to satisfy you is going to require that, or get overturned nearly immediately, especially as the SCOTUS drifts to the right.
Hell, there isn't nearly enough support for my own fix, which would be periodic mental health screenings though schools to try to identify troubled kids early, flag them as not being allowed to purchase firearms, and leave the 2nd alone. The decision would be appeal-able, though it would require successfully clearing a mental health screening.
Double hell, there's not even enough support to provide funding to physically secure schools!
Either of those are far more plausible than changing 2A. Even if I thought it had a chance of passing, I'd have to consider any 2A edits extremely carefully. It serves a purpose, and there are those that will abuse any power that comes to them.
