I still have a small bag of bullet shells from when my brother asked me to make cufflinks for his wedding. I recently used one to make a flower. Here’s another try at making use of old shells.
I hammered the shell onto a socket bit and then mounted the socket into my drill press. I used a pipe cutter to remove the primer end. I then removed the primer itself and placed the piece of shell onto an earring backing. These backings can be bought at any craft store.
I took an air gun “BB” and hammered it flat just enough so it sat in the hole left from removing the primer. After it was all soldered in place I used a center punch to simulate a firing pin mark. I didn't use the original primer because I waned to keep contrast between the metals. Polishing the original primer removes the nickel plating and leaves behind a brass finish.
Use expended cartridges. That means bullets that has already been shot. Do not under any circumstances use live ammo.