IMHO, do a dedicated. Swapping uppers is not as quick as it seems b/c you need to change the buffer, add a buffer spacer (or use a longer 9mm buffer from a custom maker), and in all liklihood you will need to change hammers unless you get your bolt moded to a ramped bolt and use an M16 hammer.
Lowers are inexpensive. Go dedicated - much more convenient.
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For the cost, it was worth it to me to use a dedicated platform.The 9mm hammer and buffer work fine with the 223 bolt, and the mag well adapter takes seconds to install or remove. I've had several of both configurations and if I went with a dedicated 9mm lower, it would be one that takes Glock mags.
I have a Rock River dedicated 9mm lower that I used for my latest build. Having used one, I wouldn't do it any other way.



























