I’ve had an Olympic 9mm upper for years. I run mine with the Socom Mfg. mag block, which allows the use of unmodified sten mags. The Olympic upper doesn’t require a different hammer, just swap the lower from your .223 gun and go. Mine runs flawlessly with a JP trigger and a full size hammer. The big pluses of the Olympic/Socom system are the cheap ($3 each) 32 round Sten mags, you can use your standard AR lower, and they run great on the cheapest 9mm ammo you can get (Wolf, Brown Bear) . The biggest thing against the Olympic/Socom setup is the different position of the magazine catch. Also, getting the last 10 rounds in the mag without a mag loader is tough. I’ll admit, Olympic had problems with their stuff 10 or 15 years ago, but everything I’ve got from them in the past 5 years has been great. The Olympic rifle that takes Glock mags would be a great way to go. The 32 round Glock mags are fairly cheap, easy to load and the mag release is back in it’s proper position. I run a bi-monthly, high round count, pistol caliber carbine match at my local range and there are a half dozen guys using the Oly/Socom system. Everyone is happy with their reliability and function.