I had a recent bullet/brass mystery but it was much easier to decipher than this one. Recently I came across a big can of nickel .357 brass I forgot I had. I remembered it was given to me a couple years ago and since I am short on brass cases I decided to prep and use it. Anyway while resizing one case it was tight and would not feed all the way up in the die. I stopped when I realized this and backed off and when I looked inside I saw what appeared to be a bullet with a flattened nose like a JSP. Well long story short. I took it out to my band saw and cut it lengthwise and discovered it was a 9mm FMJ bullet nose in the .357 case. Who knows maybe the original owner dropped a couple bullets in the can (I found one more) or maybe an inquisitive kid got into dads reloading stuff and discovered the bullets and the brass fit together.