Hi guys,

I just picked up a RRA 9mm.  I am in the process of filling out my SBR paperwork (form 1).  My question is, if I ever decide to pick up a .223/5.56 SBR upper, will it function properly with a 9mm lower?

I know the hammer is different, so would I have to change the hammer to a standard .223 hammer?

Standard AR hammer will NOT function correctly with 9mm upper/bolt assembly if your bolt is designed like the Colt 9mm version.  You'll need to locate an M16 hammer and file/cut the "hook" (used to catch the sear) from the hammer.  After you remove the "hook", this modified hammer will function with both 9mm and .223 uppers.

Before you begin, make sure you have the smaller dimension FGC holes in your lower or the modified M16 hammer will NOT accecpt the larger pins.

Hope that helps.

Joe Black has the hammer you need .....look him up...