Some states already have a form of registration where their state police get a record of each gun sale. My state does this. Local cops can access the database. They don't call it registration, but it is.
Each gun is registered at the Factory when it's made. It's already registered by the time buy it. I don't find a thing wrong with this as it's a way to track a weapon used in a crime to see how it was illegally obtained. If this is used properly it helps to get illegal firearms off the streets, out of the criminals hands, and tracks it back to the source that sold it where it ended up in a criminals hands.
In those states that do keep those records, those records are sealed and not assesable to any law enforcement without a proper court order. If it's to track a normal citizen, that order will not be given. But if it is to track a weapons used in a crime then that is probable cause to obtain that search warrant.
