Mandatory note that the AR-15 is just "Scary Black Gun" and that gun control efforts would be best served by focusing on features and accessories (and especially, actually fucking enforcing licensing and background checks) that actually increase lethality or mass-shooting potential of a gun.
... but the AR-15 fetishism by gun control opponents is cringe anyway.
I found it but there's a pay wall now
Inside The Federal Bureau Of Way Too Many Guns | GQ - https://www.gq.com/story/inside-federal-bureau-of-way-too-many-guns
A couple of points:
First, when they cite the number of deaths for 2014--33,599--about two thirds of those deaths were suicides. Keep that in mind; when someone says gun deaths they're almost always including suicide in that number. If they say gun homicides, that's the people killed by someone else, either intentionally or negligently.
Second, the article makes it seem like the idea of gun confiscations are a fever dream cooked up by the NRA. And yet, states like New York, California, New Jersey, Massachusetts, and Illinois have passed laws banning certain types of firearms entirely. A registry allows those firearms to be confiscated easily, and, if the law is overturned as unconstitutional, well, too late: your gun was already melted down,
Or, let me put this another way that hopefully seems more plausible to you, given the current political climate.
When you fill out a 4473, question 12.g. says, "Have you ever been adjudicated as a mental defective OR have you ever been committed to a mental institution?" Let's say that tomorrow congress passes, and Trump signs a law that says that anyone that has ever received any treatment for gender dysphoria, or who identifies as a gender other than the one they were assigned at birth, is mentally defective. That means that instantly every single transgender person is now mentally defective, and any that have armed themselves for self-defense now illegally possess firearms. If you had a central database of registration information, it would be stupidly easy to see which trangender people had previously-legal firearm, and then both disarm them, and prosecute them for illegally owning firearms as a person that was mentally defective.
As it stands now, you can't even look up a person's name; you can only start with the serial number, and work your way down the chain from the manufacturer to the store that sold it. A crime has to have been committed first, and you need to know what the gun is first, rather than being able to directly look up who has what firearms.