Well, let me start out by saying this is my second attempt at getting a 9mm AR up and running.
The first time was around a year and a half ago. I tried to get dependable operation out of an Olympic style. That never happened. I tried a lot of different things but I couldn’t get through two 30 round mags without a malfunction. So after about a year I sold it.

Now to the present. I’ve recently bought a RRA 9mm upper, the mag block, buffer, stock spacer, 9mm hammer and 8 uzi mags.
I put all the parts [hammer, buffer, stock spacer ] in a RRA lower that I assembled over a year ago and had a 20” flattop upper in.5.56mm on that has run over 700 rounds without a malfunction. Not one. The fit and finish is very nice between the old lower and the new upper.
After getting everything together it pasted a safety test and looked good. I found a couple of the magazines to be easy to work on with hand tools, so I notched one out with a file. It fit good and feed by hand very nicely. I did find the magazine fit in the mag block to be rather loose. But the magazines where in pretty solid in regards to the magazine catch.  
So after I have a buddy run the rest of my mags through his CNC  for the mag release, out I go to his back yard for testing. I loaded 7 magazines with 6 or 7 rounds each.
Immediately the trigger group will not reset. I smoothed and polished the hammer hook for the disconnector and the disconnector hook. After that the trigger reset was fine.

The first 2 magazines went fine, then I started to get FTFs. I had to readjust the mag block. I had to do this 3 times. Today, I ran a set screw through the receiver in to the mag block behind the front takedown pin. This was suggested by another member here at AR15.com. I find this to be a very nice way to hook up a dedicated 9mm lower. The magazine block is in very solid now. I think I’ll have it permanently pinned in the near future. So back to the range, now I think I have it going on. BAMM FTF again. The magazine has to much room to move around, if I hold the magazine back on the bottom it runs fine.
I just finished modifying the magazine block by running a set screw though the back of the block to keep the magazine from moving around to much. This keeps the magazine from moving past the magazine stop on the bottom of the feed lips. I think this will take care of the FTFs . I’ll be at a range tomorrow to see where I’m at. I’ll post again to let you guys know what else I need to do.
A buddy of mine has Colt Factory mags for his 9mm. Maybe I’ll be able to check my shooter with his mags to see what I’m missing.

Mark, Good job, Everything you've ran into is fairly normal,I *may* have been the one to suggest the front pin set screw,As I've did this myself,I've also found that Uzi mags are a little loose in my block,...The Last FTF issue may be a mag catch position problem,If it cut to low it will position the mag to high in the block and the mag will rub on the bolt slowing it down,Hence FTF..Hopefully it was the mag block issue that you've addressed.I found that the RRA block will "ride up" no matter how tight you crank it,Sooner or later it will ride up into the bolt and as above,FTF....Keep us informed.......UNDERDOG

I went to the range Sunday, I managed to fire several rounds out of my 9mm AR then I started to have failure to eject problems. I adjusted the ejector and tried it some more. Still fte problems. After removing the bolt I could see the extractor was not aligned correctly with the bolt face. The pin holding the extractor in place had moved up in the bolt. After dapping out the pin and cleaning up the extractor channel and the extractor, I reassembled the bolt and started to have a good deal of fun with my AR.
After 500 rounds, I have found two magazines to be 100% functional out of 7 magazines that I’ve had modified.
Tonight, I cleaned all the magazines and was really surprised to see how much crap was really in there. This cleaning may up my percentage of useful magazines. I’ll find out my next trip to the range.
Getting back to the extractor pin, I was really surprised to see the pin used is made out of a really thin piece spring steel rolled up make a roll pin. I’m going to replace it with a roll pin that is made out of a single piece of wrapped steel that has a split in the side. I’m not really explaining this in the clearest manner. I’d post pictures if I had a server.
The best part of this deal is I can see some light at the end of the tunnel. It’s a small speck of light but it’s better than my last try.  

One way to "fix" your problem with the RRA block is to buy a ASA block.  After many hours of reading on this board, I took the plunge and bought a new ASA upper and block.  It didn't run immediately because I was trying to use USA mags.  I bought some of the 25 rounders from Cole Dist., modified them, and ran into another HUGE problem: NOT ENOUGH AMMO!!! [heavy]

J

So what is the difference between the ASA block and the RRA block......(not to hijack the post) but if I have modified uzi mags based on an RRA block what is the chance that they will fit the ASA block.....will the ASA block work with an RRA upper....

The main difference is that the ASA drops in from the top.  It is a snug fit with NO play.  The modified mags should work in both blocks, but I would try them because there can be [i]some[/i] difference in mag heights if I understand correctly.  I heard that the RRA blocks were loose and that's why I went with the ASA block.  You have to use the IMI mags instead of other contract mags because other contract mags seem to be a little thick front to back and won't fit unless they have been surfaced.  I did that with one, and I didn't like having to do it.

I bought the 25 round $9.95 IMI mags from Cole Dist. and I haven't had a problem with fit or function.

Again, I LOVE MY ASA BLOCK. It runs GREAT.

Just my [s]$0.02[/s] $0.03.

J