I have a few dollars invested in a blockchain solution to gun registry called "trig".
http://www.blocksafefoundation.com/
The technology is in its infancy, but blockchain technology is IDEAL for something like gun registries. It's simple, it can't be hacked or edited, and the applications of the registry/actual firearm are pretty unique.
The idea behind it is once the firearm is registered to someone, it cannot be fired by anyone else. You can also track the actual firearm being used in real time, and disable it if it is equipped with the digital technology.
Of course tall of this is only whitepaper, but the technology is coming. Hopefully soon.