See post number 6 please.
It is not registration. Not even close. The form you fill out when you buy one new is the end. You take the gun home,, play around with it a little, and decide you don’t want it after all. You can then legally sell it to a friend or stranger with no paperwork.
You have no requirement to notify you sold it. The friend has no obligation to notify the government that he has accquired it. The government has no list to point to that they can then demand you account for the whereabouts of any gun.
That is what registration looks like.