I'm planning my first 9mm build, so far I have a RRA lower which will be registered as a title 2 firearm. The build is going to be a supressed SBR.

I am planning on using a Hahn mag block so I can use the lower for both 9mm and .223 SBR's. Do I need to use the 9mm hammer, or will the standard hammer work? I haven't purchased a 9mm bolt yet either, is there a prefered brand for reliable function?

I also read somewhere that you cannot install a two stage trigger in a 9mm lower, is this correct? It seems that if you used the stock .223 parts kit a two stage tigger would not be an issue.

The Gisseler 2 stage works. I would use the 9mm hammer with some JP yellow springs that Brownells sells for 10 hole $. That is what I use and the trigger feels light. I would just buy the bolt with the upper like from Adcofirearms when they get them in stock . MY gun runs great it is all RRA build.