Ok. The FAQ doesn't help me on this one.  
I see from pics that the blocks for Oly uppers use a toggle bar under the mag well to drop mags.  The Colt style (Hy-Teck block) uses waht looks to be a push button.  Is it left side activated?  

From what I can tell neither type uses the std. AR mag catch.  If they're the same (left hand operated) and neither operates the bolt hold open, then the root of the decision is whether you want to dedicate a lower for 9mm with a colt system or to get teh Oly and be able to easily swap uppers (.22lr, .223)

These are things I think are right, anyone with either system let me know your experiences, opinions and where I'm wrong.  

I have a dedicated .223 20" A2  and a DPMS .22 on another lower that I'd like to put a 9mm on.  

TM

Oly uses standard magcatch/drop if you  stick to the converted Sten mags that they sell.  Mine uses regular sten mags with paddle release on magblock.  Hope this helps.

D

Quoted: Ok. The FAQ doesn't help me on this one.   I see from pics that the blocks for Oly uppers use a toggle bar under the mag well to drop mags. Only if using plain Sten mag and a filler block (SOCOM) The Colt style (Hy-Teck block) uses waht looks to be a push button.  Is it left side activated?   The Hy-Tech is held in via the std AR mag catch, the paddle release on lower left duplicates the Uzi mag release, so you use Uzi mags as-is. From what I can tell neither type uses the std. AR mag catch. OLYMPIC---->Only if using the Sten mag with the tubing on the mag, then std AR release is used. COLT---> Only if using a COLT pattern block, and mags retained by AR magcatch, like std 9mm mags from COLT or with UZI mags with notch cut to duplicate the COLT mag.. If they're the same (left hand operated) and neither operates the bolt hold open, then the root of the decision is whether you want to dedicate a lower for 9mm with a colt system or to get teh Oly and be able to easily swap uppers (.22lr, .223) There is no dedicating the lower for 9mm, I have a std lower set up, and swap uppers all day long.  Just depends on how you choose to occupy the space in the magwell These are things I think are right, anyone with either system let me know your experiences, opinions and where I'm wrong.   I have a dedicated .223 20" A2  and a DPMS .22 on another lower that I'd like to put a 9mm on.   Soooooooo, slap a 9mm on top of one of them and be done with it TM

Std lower;


Something to fill the magwell; ala Hy-Tech block---


Add an upper; ala Colt pattern ---