Marty,
Perhaps you could seek advice from a doctor/ emergency medical professional/coroner. I would imagine survival/extend of injury would depend on a number of factors which would include:weapon used,calibre of bullet, angle,distance of shooter from intended target, health of victim, weather any major arteries were hit, access to medical attention/triage, knowledge of attending,exposure to disease/infection...etc...
Good luck with your book.
SOH