Few people would bring an illegal firearm into NYC or other major US metros because a) the penalties in most of those cities and states can be brutal and b) it's not that difficult to acquire a legal firearm in most cities. If someone's smuggling a gun it's likely because it's just a small part of more varied criminal activity. Or because they did it by accident.

Also, I find it unconscionable to suggest we should allow home manufacturing of automatic weapons without even engaging with possible ways to stem that tide.