I can only speak for Baltimore but there are people here making and selling guns made from 80% lower receivers and tiny pieces of 3d printed plastic that will make your gun fully automatic. Just last month there was a Baltimore city police officer who lived in the county caught trading guns and internal information for drugs. If police officers are doing it you can believe that regular citizens are doing it.
There are people who are traveling right over the state borders to DE, PA, and VA to buy 30+ round magazines and come back and sell them to people in and around the hood. There has even been 3 shooting this year involving AR15's. One of them involved a fully automatic less than a 1/4 mile up the road from the state police barracks and county courthouse.
Easier access to a gun that you believe is untraceable leads people to be more willing to use them to commit murder. The fact that they only cost around $500-$700, a couple hours of youtube instruction, and you have a cheap tool to commit murder and robberies with. The only saving grace from all of the DIY pistols is the high failure rate for them to jam because of poor construction. And the fact that some of the people illegally carrying haven't practice shooting very much so they have crappy aim.
I was one time shot at for no reason other than in the wrong place at the wrong time and the guy who was just robbed thought I was part of the group that just robbed him. Another time I was trying to stop a violent robbery behind my house by yelling at them from my yard.