How to reduce the amount of weapons in circulation and yet not infringe on rights to bear arms? The solution is to impose excise tax on all gun sales to raise the bar for entry. Subsequently, the govt will use the tax revenue to support buy-back programs to reduce the amount in circulation.This is akin to how the govt treated the tobacco industry.
This method neither infringe on people's right to bear arm (as long as you can afford it) and yet encourage people to give up their arms voluntarily. It is a win-win.