[Rick Lee]

I dunno about that Charles. Extractors do leave marks on casings and they are very distinguishable under a microscope. Now, if the casing has been reloaded a few times, then it would be pretty tough, since there would be multiple extractor marks on it. And extractors do wear down, both in springiness and in lost surface area. I've recently replaced the extractor in my SIG P220 after about 11k rounds and 10 yrs. But brand new factory ammo would probably be pretty identifiable. Now, I'm pretty sure some of my guns are customized way beyond any hint of factory specs, so that a ballistics expert would only be able to match casing and gun if he also had the gun.