The trouble with the argument about gun violence being significantly lower in strict gun control countries is "cherry-picking" the candidates. Japan has restrictive laws and low gun crime; Great Britain now has the same laws, but a troubling rise in gun crime. Mexico has very restrictive laws, but a huge gun crime problem. And, countries like Norway and Germany have tough gun laws which did not prevent nut-cases from getting guns.
As for "sensible regulations" in states or cities, those almost always run afoul of the 2nd Amendment. Witness the Heller v. Washington, D. C., wherein the Supreme Court struck down such "sensible regulations."