A few years back I was walking around a gun show and saw two, five gallon buckets filled with loose ammo under a dealer's table. I asked him if it was for sale and he said it was. I ended up buying them and taking them home. Once I reached my house I began the immense task of organizing all the ammo. I started to realize that ther were quite a few different types that I had never seen before. This is one of them... It is some sort of rimfire cartridge. There is a "U" headstamp on the back, im guessing for UMC / Remington. I was thinking possibly .30 rimfire short? Is this ammo worth anything?