I am thinking of building a new AR using a RRA 9mm upper.  It appears that I need to buy the upper and the $150 mag block.  

-I guess I use a regular AR lower?
-What kind of mags does it use?
-Am I missing anything?
-Any owners out there please comment
-and lastly pics,pics,pics!

Here is some info that I got from Pete in NH regarding what one would need for a 9mm AR (aside from the upper of course!).

RRA lower with a 9mm hammer, 9mm buffer, and 9mm mag block.

*Note that RRA's 2-stage trigger will not work with a lower configured like this*

As far as mags go, the RRA 9mm ARs will accept modified UZI mags and I [b]believe[/b] 9mm Colt mags, but I am not sure on the Colts.  You would be able to find some on the EE and I think Pete may have some.

I do not have one currently but I have been studying the components of one for a while now.  Hope this helps!

Standard AR lower. If semi only, you will need to either ramp the 9mm bolt for the semi hammer or use a tailless M16 hammer. If using on an M16 all lower parts are compatable. It is designed for either a modified Uzi mag or a factory colt mag which will hold the bolt open on the last round. The uzi mag wont do this.