How is it possible? Logistically, I mean. You can't go searching every person's house.
Lets assume all the responsible gun owners stash their guns. Because they're responsible law abiding citizens, they never take them out because having a gun is now a crime. (Hypothetically guys)
Violent crime and gun crime would still happen, but gradually, the majority of guns used in those crimes would be confiscated (after the fact), gradually reducing the rate of gun ownership among criminals, until they start stashing their own firearms.
Less guns in the public eye, less school shootings, less gunpoint robberies.
Eventually you have a generation who grow up in a different culture (50 years like you say), where guns are scary and illegal. Eventually, the cons of having the stashed guns outweighs the pros for this newer generation, and they quietly dispose of them or anonymously donate them to museums.
Its a culture change, like you say it may take 50 or even 100 years to completely eradicate guns, but it is "possible".
All of that being said, I don't like the idea of being a victim in the mean time. I'd much prefer a gun culture to a nanny-state culture or a victim culture. Spree shootings are horrible but banning guns is not the answer. I know this isn't a political thread but I just thought I'd put the disclaimer in there so there's no confusion on my position.