I have
never forgotten that I owned a particular gun.
I have, however, forgotten where I put a particular gun! I "lost" a Ruger .22 for a couple years one time. Knew I had it, but couldn't find it. Finally found it, disassembled in a grocery bag in a back bedroom, where it had wound up after my son-in-law returned it, disassembled.
Told the stupid ......not to take it apart! He did, anyway. Daughter has since come to her senses, so I don't have to deal with him any more. And no, he never got to borrow anything else, except her.