I think firearms designed to kill humans should be illegal. Handguns, automatic weapons, maybe even semi-automatic. Single-shot hunting rifles and shotguns are typically designed for hunting and can't really be used for mass shootings.
Hunters will also never give up their guns, and it will be a disaster, like the long-gun registry. They'll bury their guns before giving them up.
Well burying them would be one effective way of curbing gun crimes.