I have assembled 6 AR 9's.
The best value IMHO, is Joe Bob's / NFA.
It WORKS.
And Real Glock mags, WORK.
You cant say the same for every Colt system mag.
I started with Colt system on my registered Sendra M16.
That was way before Glock System came on the scene.
The advantages to the Colt are, it can use the 100RD. BETA mag.
And it can be used on a G.I. type lower and it has LRHO on the lower.
The barrels are the same, Colt or Glock.
The bolts are different, and you MUST use a ramped bolt
Now you can buy a bolt that will work with no machining.
Get one that works with Glock AND Colt mags.
They are now factory ramped.
Joe Bob's sells everything, very affordably
Their lowers are GREAT.
You will easily assemble a reliable AR9, for a fraction of $1000