The 9mm bolt is a "lot" heavier than the .223. Haven't measure it, but you can tell its heavier. The buffer is probably heavier too.

Since the inside-diameter is larger, the barrel should be lighter than a .223 of the same outside-diameter.

I've got a rifle-length PRI tube along with a Cavalry Arms lower on one of my AR-15's and I really like the light weight. That's what got me thinking about one for this.