I just realized that the polymer80 AR lower comes from the same town that I just moved here from in cali. I'm totally going to have one of my friends swing by their shop for me.
There is a registration, albeit a highly inefficient one. Once a firearm is manufactured and has a serial number, the information (numbers, make, model etc) goes to the ATF, as well as info on which licensed FFL they distribute it to (same process on suppressors and other class 3 toys. From there, they look up who the firearm was sold to via the 4473 you fill out when purchasing. Now this is all done by paper, but it is there. That's why most of my guns were bought privately.
But ya know is the boys in blue ever come knocking, all I'll have to do is inform them about my tragic boating accident...