Let me suggest something --as an owner of firearms: Just require a permit to own an assault weapon just like what is done now with handguns.
It will not stop illegal ownership and criminal use of handguns and assault rifles but it will prevent nut-cases from buying an assault weapon and the next day going postal is a crowded venue like that gay bar this weekend in Orlando.
And don't start a war you cannot finish
This is exclusive of domestic terrorism (I guess?) ...