[cashflyer]

I could be slightly off since I am no expert on forensics, but these are my thoughts:

I don't know of any way to tell if a .38 was packed with a round nose, wadcutter, hollow point, etc. The case is just a case.

As for a semi-auto, the way the rim is made is often an indicator (but there are exceptions) and you can sometimes see the extractor mark on the case after firing.

As for knowing if the round was fired in a Thompson 45 vs. a Colt 45, you probably wouldn't know it casually - if at all. Unless there is a distinct feature about one's firing pin.

I can usually pick up 7.62x39 brass and tell you if it was fired in an SKS, simply because SKS has a crappy stamped metal firing pin that leaves a distinct mark.... which can be eliminated if it was modified/upgraded.

Some rounds are unique to the type firearms that use them. The 7.62x25 comes to mind. It was used in only a few types of communist block pistols, narrowing down your choices a lot. You could never look at these and say, "I think these came from a Browning automatic."