I don't think they changed the operation of the rifle at all. The did do a lot to the lower though. It's now polymer rather then stamped metal and it uses AR15 mags, mag catch and fire control parts.
The design inspired the current rifle used by the Brits (SA-85? they keep changing the name and I can't remember what it is - help!).
BTW, internal parts are stamped and this makes it easy for the "home" gun plumber to replace parts if necessary. Take your measurements, make template which is glued sheet steel of same thickness, drill out & hacksaw rough outline. File to finish and harden with casenite.
Is the AR18's action same as AR15 or different?
That point is important to poor souls like me in PRK, if it's AR15 action, it is automatically banned(even 22LR is assault weapon here, YUCK!!! )
Well johnAK you can tell by looking at it that there is no way any one in the RPK is goin to be able to get one, sorry
if you have not seen the photo you go to http://www.armalite.com it's at the top of the frist page.