I'm not much of a bullet guy so I won't venture a guess.
There are several guys who frequent this forum with lots of knowledge on the subject, however they will likely need precise measurements to have any chance to ID your bullet.
Without any accurate measurements with calipers or even something in the picture to give it a size reference it's really hard to tell....
all of that said, My best guess by the picture is a spent 22 long rifle slug.