If I found a loaded firearm, it would quietly go into my collection.
A distant relative of mine decades ago did that exact same thing in Moline IL where he lived. When he died his daughter sold the gun to someone who went to register it in Michigan, but then the SHTF when it came up stolen and ballistics matched it to the former owners murder during a robbery way back when in IL.
Just be careful is all I'm saying, just like with a new girlfriend you really don't know where that thing has been and done before you got it.