TheLaw ... next time you see me remind me and I'll give you the A-zoom ones I have. At one time I had them in all calibers. I am not sure what I have remaining but will check if you call me this evening to remind me. Don't buy any yet as they aren't cheap.
I don't use any snap caps or dummy rounds at all for normal dry fire practice. What I mean is I don't use them for the purpose of protecting part X or part Y. In fact, someone I trusted (but can't recall who at the moment) suggested the poly ones were just as good if not better as they weren't as rigid ... even if they don't have the springs.
I have a few of the poly ones from a previous class and use them for re-load practice, etc. when I need a round in the mag or to setup double feeds, stovepipes, etc.
The ideal setup would prob be for someone to re-load a few rounds with no primer and no powder ..... real brass and real bullet. The only potential would be the fact they would look like a live round and if you were to get confused could get a BANG instead of a CLICK. I would suggest using high contrast paint pen and marking the dummy rounds if you choose this method.
The only issue I have with the poly rounds is they do get chewed up after a bunch of malf clearance drills (esp the .223/5.56 rounds). Once they start getting deformed or scuffed up to the point of poly shredding off I suggest discarding them immediately. You don't want that stuff getting jammed up in your weapon.