When I was young, you wouldn't know if someone had guns unless you went hunting or something. It was kinda taboo to inquire.
This ethic probably originated from the fact that guns have always been a target for thieves. Nowadays, gun bros post their weapons on Facebook so you can see their custom paint job and accessories.
Building a database of gun ownership would be trivial. Even the old timers with their secrets could probably be sorted out from a dozen other personal data points.
Sorry gun owners, your collection is everybody's business, just like a uterus.