How do find out the owner of guns?

Answer 1

In the U.S. there's no real way to find out. There is no federal registration and most states don't have registration.

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Actually all firearms sold by federally licensed gun dealers (FFL's) can be traced via their serial numbers by government agencies such as the BATFE and not individuals. FFL dealers are required to maintain records of sale and serial numbers for as long as they are in business. A particular firearm can be traced from the manufacturer to all wholesalers (if any) and to any FFL dealers involved in the sale(s) and to the individual purchaser. After a FFL dealer goes out of business they are required to surrender all of their records to a BATF office where they are maintained in perpetuity in violation of our Constitution - this outlaw federal data bank constitutes a form of registration which is clearly unconstitutional.

Individual sales of course cannot be traced or tracked as readily.

However, an FFL holder can destroy the 4473 forms after 25 years. And, if the OP was referring to an individual finding out who owns a gun, generally, an individual cannot call up a gun dealer and request information on the person who bought a gun, unless the FFL wants to open him or herself up to a lawsuit for violating privacy laws. In addtion to that, the ATF only does it under certain circumstances, such as, they are trying to trace a stolen gun.