Liability like car ownership. Failure to secure your weapons imparts liability. Guns stolen or sold without a background check that are used in a crime carry a punishment for the last registered owner. Punishment ramps up rapidly with multiple offenses. This will punish traffickers but also encourage safety.
Correct. For one, it should be mandatory that care be taken that guns not be stolen. Locked up in safes when possible or otherwise attended to and not left lying around. Secondly, a missing gun should be reported immediately. Like I said, punishment ramps up after multiple offense. If it happens once, call it a fluke and fine $100 or whatever. If it happens twice you're being careless. If it happens more, you are probably a trafficker and should be prosecuted and lose your right to own guns. This kind of rule will affect very, very few people and hopefully zero responsible owners.
Presumably only if you fail to alert the authorities to the theft.
Of course authorities don’t always pay attention to registration changes — one UK police force sent me a speeding ticket for a car I had sold nine months previously, even though the DVLA had actually registered the sale and transfer of ownership.