. . . .
I drove the rifle to the FFL the next day and found the owner in the process of locking up. They have apparently switched to extremely short hours. I explained the situation, explained that they needed to contact Century for the return, and stood there while he opened his phone and found my email. He accepted the rifle and said it would ship out the next day as soon as they could find a box.
. . . ..
Am I understanding correctly? You gave the guy a $700 rifle and got no receipt of any kind? I see no mention of a receipt, or any other paperwork, completed at the time when you gave the rifle to FFL for shipping back to Century.