I'm not so sure it would drop by that much. Maybe like 40-50%, which is still significant enough. But yeah, you're right, it's not gonna happen until there's a political will to modify or eliminate the 2nd amendment.
So I was basing this off of a comparison between UK's homicide rate and the US's. The US has a homicide rate of 7.8 per 100,000 while the UK has a homicide rate of 1 per 100,000.... so 8x lower. Now the UK is not a perfect substitute for the US, they have stronger social safety nets, and a more homogeneous society (although there is a fair amount of diversity, it's less than the US), and some of that no doubt contributes to the difference, so I said like 70% instead of 90%.