What does "yours" even mean? Do you mean ownership? Ownership is a VERY complicated concept. My favorite explanation comes from our old real estate lawyer: Ownership is a bundle of rights. They typically transfer at different times, and due to different causes. Some of these come from black-letter law (today mostly the UCC, as adopted by pretty much all states in the US). Others come from common law (British tradition). Some come from precedent cases. Simply saying "yours" or "not yours" is a dangerous oversimplification.
IANAL, to I won't give the long lecture here about what really happens. And if you asked a lawyer, they would probably refuse to do so, until and unless (a) you pay them a few thousand $, and (b) they are in an attorney-client relationship with you. Or you could read any of the standard civil law textbooks, which have several chapters on that topic alone.
And that makes the concept of "ownership" even more complicated for things that need to be titled or registered, such as real estate, air planes, vehicles, and yes also guns. If you give someone $$$ for a gun, and take possession of it, and the check clears, and you put it in your safe and shoot it on the range, but you never do the required paperwork (some combination of 4473, DROS, PPT, OpLaw, ...), is it really yours? No, it is not completely yours. Unwinding this partial transaction is not easy, and we get back to the advice of hiring a lawyer in a situation where this causes conflict.
If it is that easy as "explicitly says", please quote the statute. I dare you ...
EDITed to add: While I was typing it, Constitutional Armory doubled down on his allegation, still without any supporting evidence. My dare stands.