I haven't seen much discussion on ZM Weapons AR-based designed recently.  According to their website, it sounds as though it is indeed piston driven?  And yet, I think I recall someone saying here that it is still direct impingement.  Which is it?  Might there be a schematic available somewhere?  Has anyone used their collapsible stock?  (The side-folding, 5 position collapsible that they call the "Tele-Folding?)I have already heard that it is a heavy design, but I'm still interested.  Here's a link to their offerings.  http://www.yankeehillmachine.com/store/lr.html  Thank you.

It's a hybrid. The gas tube is attached to the key and the action spring is wrapped around the barrel. Cleaner, and you don't need a conventional receiver extension, but its proprietary, and accessories are limited. There may or may not be other issues I am not aware of.

Thanks Combat_Jack.  When you say it is a hybrid, what exactly do you mean?  Does it actually have a piston?  Because, what good would it do for the gas tube to be attached to the key as you say?  Anyone have any firsthand experience?  Thank you.

I think Jack means the action spring is wrapped around the gas tube/oprod, the oprod is on top of the barrel.  As to it being cleaner, gas still gets blown on the bolt.  It's no piston though.
Their folding stock is patterned after the FN, it's a solid and fast design, beats the crap out of Ace's folding mech.  It's heavy though.  The folding and LOP adjustable stock is nice, again kind of heavy and made of all metal, could be a problem in freezing weather (face stuck on the stock lol)

Go to this thread to find more info and pics

Thank you Duffy.  The link you posted was most informative.  Now, I've just got to pony-up for a membership so that I can view all of the archived info.