Don't know that is a completely true statement aftershock.. I'm fairly sure that most 9mm uppers will work with AR lowers that have the stock trigger and hammer set. Depends on the manufacturers specs on the BCG.
I spent some time thinking about this kind of setup as well, just a diff upper, but honestly, for a few hundred more you can get a complete weapon in 9mm. If you shop it a bit, you'll find they run about $200 cheaper that a regular AR.
thats what i got from the RRA website ....if you go on their site and click on the pic of the 9mm upper the conversion info window pops of what they say you need....i am sure different companies have different options...i believe with a ramped bolt there is no need to switch the hammer...but i could be wrong
There are 2 different 9-mm pattern uppers. With the Colt pattern upper you need a modified hammer or ramped bolt carrier as well as a mag block or modified mags. With out the modified hammer or ramped bolt you will jam the gun up good and tight. With the Olympic arms pattern a standard .223 config lower will work as is. You will just need a modified Sten mag (one comes with the Oly upper) or a Hahn block and unmodified 32 round sten mags ($4 each from Tapco).
The model 1 block is for Colt pattern uppers. The Hahn at about 1/2 the $ is for the Oly pattern Brownells carries this block.
Leeindy drop me a PM if you need more details. 9 mm AR's are a hoot to shoot.
This is a Oly carbine flat top upper mated to a Superior Ams lower built with a mil spec lower parts kit and a 6 position Tapco stock. The small lever coming out of the bottom of the magwell is the mag release on the Hahn block.