Very common. Since the wound was abdominal from what I hear, I'm guessing it lodged near the spine. But even if it didn't, it's still very common for doctors to leave it in place. You can cause more damage trying to extract it than just leaving it in place.
one wouldn't intuitively think that a ragged piece of lead floating around in there would be particularly healthy.
i'm wondering what, if any, kind of id can be accomplished via xray or other external device.
i'd imagine they might be able to estimate caliber, but not much more than that ...