BJ wasn't looking for shell casings. Most likely, she was doing her best to try and keep some of her thoughts together. Which I would think that would be a great task, finding two relatives dead. Chris had two shots to the head, and Gary had three. There's no way either of them could have crawled anywhere.
https://www.google.com/amp/www.grunge.com/32897/people-amazingly-survived-gunshot-head/?amp=1
https://www.ncbi.nlm.nih.gov/m/pubmed/8239201/
A quick google search reveals that only 66% of head shots end in mortality. Even 25% of people that shoot them self don't die. I agree multiple shots to the head your dead. But if any of these numbers are remotely realistic it would indicate there is a possibility someone could easily survive a short time and potentially drag themselves a shot distance.