Here is an interesting poll from PoliceOne.com.
Virtually all respondents (95 percent) say that a federal ban on manufacture and sale of ammunition magazines that hold more than 10 rounds would not reduce violent crime.
The majority of respondents — 71 percent — say a federal ban on the manufacture and sale of some semi-automatics would have no effect on reducing violent crime. However, more than 20 percent say any ban would actually have a negative effect on reducing violent crime.
The overwhelming majority (almost 90 percent) of officers believe that casualties would be decreased if armed citizens were present at the onset of an active-shooter incident.
An interesting read.