I would not trust that method because if all the marks on the bullet except two extra marks match up they might say it was a match. Cops lie for each other all the time and make tests come out any way they want to for each other. Also the extractor and ejector can leave identifiable marks on the shell casing. I suppose your friend must have had a real busy day having to kill 4 or 5 different people? I know they can't get any ballistics from a shotgun shooting buckshot if you keep your shell casings.