Incredibly difficult but not impossible. However what will be impossible would be for LAW-ABIDING citizens to arm themselves if that was to be reality.
Criminals will ALWAYS find a way to get their hands on guns. NO LAW WILL PREVENT THIS!
Cops aren't perfect I would rather civilians arm themselves and be PROACTIVE in preventing crime rather than expecting officers to always put their lives on the line for their sake. (I am thinking about officers lives and safety)
The only person, worth protecting you, should first and foremost be yourself.