I suppose weighing them would be another way around my mystery hunter. It would take a nice electronic scale to make it viable and not time consuming in my opinion, and those aren't cheap. I mean... weighing each roll individually isn't the fastest process in the world... once you go through enough boxes, ripping through a roll, rim searching, and then dumping it back in the box only takes a few seconds.
Plus... although the 90% halves are substantially heavier than the clad, the 40% are EXTREMELY close in weight in comparison. Add in possible short rolls, roughed up/shaved coins, etc. and it makes it that much less accurate.
To all you MD'ers out there: any of you want to try your detectors out on some rolls of halves and see what happens? It makes sense that waving it over the whole roll would mean that it wouldn't detect EACH half seperately, so would it treat the whole roll as a single chunk of metal? Wouldn't having a silver or some silver in that chunk change its reading or display number, etc.?
The other thing that this guy at my banks could be doing is running electricty through the rolls, since the brinks rolls are open at both ends. Changes in conductivity could alert you to the presence of silver.
Who knows... this guy has just bugged me and others for so long that we have spent a bunch of time thinking about it while CRH'ing together. Still waiting for the day one of us get lucky enough to catch him dumping at a bank! =)
~Dave