Rattling 7.62x54R

So I’m sitting here reorganizing my 7.62x54R collection and came to two rounds with “U.S.C.Co. 17” headstamps. I’m trying to decide which one to keep, one is sort of bent and the other has a light headstamp. I notice that the one with the light headstamp rattles when I shake it. The other one sounds like powder inside. I think about posting here asking what could be inside, but after reading the 7.65 exploding round story below, I decide the only smart thing to do is pull out the kinetic puller and go after it. The results are below. No magic inside, just a piece of paper. Why would someone do this? The round is out of an old collection and was covered in clear lacquer. Was it just a way for a collector of the past to mess with me in the future or is there some reason this would have been done?

Maybe the guy put the paper ID inside long before he could get a magic marker to write “7.62 Russian” on the outside? Maybe it was a highly unfamiliar shape a long time ago. My understanding is that 7.62x54R was quite uncommon in the States before 1950’s, before Franco dumped captured Mosin-Nagants.

I suspect the paper was rolled up and stuck in the neck of the empty case, eventually slipping down past the mouth, then someone at some point stuck a bullet in the case.

Thanks for the imput guys. I still like the idea that someone decided to mess with a future collector, but who knows!