I’m thinking about buying a preban AR15 from an individual, but I don’t know anything about its history.  I know it was manufactured before 94, but how do I know for sure that it was assembled as a SAW before the magic date?  I also know that the person I’m considering buying from, isn’t the original owner.  How do I find out if the gun was stolen?  I know and trust the person I’m buying from, but I have no way of knowing the previous owners.

It all depends on the Manufacturer...some kept better records than others.

Ultimately, IF YOU KNOW FOR SURE that the receiver was built AND SOLD before 1994, you are safe.  Why?  Because the U.S. legal system puts the burden of proof on the plaintiff (this case, BATF) that you are out of compliance.  How is anyone to know whether or not that was made into a rifle if the original owner no longer has it?

As for being stolen, well, you might want to have a "friend" in law enforcement try to track that down for you...but that's a long shot.

If someone else on this forum knows better...please comment.