There is no provision in Federal law for LEO's to personally own post-86 MGs.
It may be issued to them by their department, and they may be able to keep it at home, but title for the weapon would be held by the Dept.
Interesting. So they have use of the weapons-including recreational use-as long as they are on the force. When they leave they must turn them in.
Seem dodgy. And I guarantee that isn't happening in all cases.