Which should be more than sufficientso you are limited to 15 + 20 rounders if you want to run OE mags.
I'm seeing them now for around $800 to $850 new. I
The lower (unless it is the new RRA lower that does not use a mag block, which may be what you mean) can be used for .223 uppers with the mag block removed and the proper buffer. Two quick changes. With some set ups you don't even have to change the buffer. Just something to think about.With a dedicated 9mm lower