Be that as it may, should any gun owner be held in any way responsible for negligent discharges caused by surrendering their weapon to a cop who demands it?
The gun owner should not be held responsible for the negligence of the cop. If the cop had been following The Four Basic Rules of Firearms Safety this incident would not have happened. Anyone with an IQ above 75 can do it.
http://mondaynightshootingleague.org/pdf/FourBasicRulesOfFirearmSafety.pdf
The Four Basic Rules of Firearms Safety*
1. All guns are always loaded.
Treat every gun as if it was loaded, at all times, no matter what.
Think and BELIEVE every time the gun is handled, it could fire.
2. Never let the muzzle cover anything you are not
willing to destroy.
Be conscious of the direction your muzzle is pointed at all times.
This includes at yourself, any other person, animal, or property
unless you are either intending to or do not care about destroying or
killing that person/object.
NEVER handle a gun behind other people or bend over with a gun in
your hand on a shooting range.
3. Keep your finger off the trigger until your sights
are aligned with the target.
Pay attention to what you are doing while handling a firearm.
DO NOT let your finger contact the trigger until the gun is on target.
4. Be sure of your target and its surroundings.
Pay attention to what is going on around your target.
YOU are responsible for the terminal resting place of the bullet,
intentionally fired or not, no matter what happened.
*Base rules from Col. Jeff Cooper, American Pistol Institute, 1977
Probably not, unless there was some intentionally negligent act associated with the situation.
If it could be proved that the person intentionally presented a loaded gun, then maybe. The exception to this might be if the person is legally carrying a loaded gun and is attempting to comply with a "no loaded guns" policy. In this case, the officer KNOWS the gun is loaded, though if he follows the safety rules, it won't matter.
Another exception might arise if the trigger mechanism has been modified in such a way that the gun has been made inherently unsafe and the owner knew this. Liability would be shared with the incompetent cop. A friend of mine let me fire his .22 target pistol. It felt like you could fire it by just breathing on the trigger. It was not a gun I ever wished to own.
There are two different scenarios that I have run across which present difficulties.
The first is when a round fails to discharge. You have to wait so that the primer becomes stable despite having possibly been struck by the firing pin. If the primer has been deformed by the attempt to fire it, then I could see how handling the gun with the defective round in the chamber could be risky.
Another situation I dislike intensely is using a revolver in single action mode. How does one safely lower the hammer on a live round? Everything about trying to lower the hammer slowly feels awkward and unsafe.