I have yet to hear of any of the rank and file failing to enforce gun laws. In fact when you read about some poor schmuck's gun collection being seizured, it's the rank and file that does it. You don't go in a career in police work because you think that some laws are stupid and shouldn't be enforced.
Unless it's part of a real crime, murder, rape robbery, etc on the part of the gun owner/collector, except in a few jurisdictions, its generally the BATFE, which aren't real cops anyway, that does this sort of thing. The bottom of the barrel in federal "law enforcement".