I am considering building an AR9mm later this year but need to do some research on the best parts to buy. i.e. which mag block or dedicated 9mm lower ? Which LPG and upper receiver ? I want to use Colt or C-Products mags. Trying to build this under $1000.

Aim Surplus Parts

CMMG Lower

Are you set on colt mags? I find value in multi purposing some pistol mags.

I'm using a Faxon 4" barrel
Ballistic Advantage has their barrels on sale ending tonight but I think it's the 8" only
I'll be using a non-F/A upper and I'd like use a JP SCS but they're $150
Look at Spinta Precision for a bolt

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

What buffer weights do you use?

I've assembled several and have had good results with Joe Bob's/New Frontier Armory for Glock-based platforms. I prefer, however, my Colt-based gun and, in particular, the one I built on a Daniel Defense SBR lower with a Macon Machine block, which is a top-loader and does NOT require the removak of the bolt release. The gun feeds smoothly and there is no evidence of abnormal wear after 750 or so rounds, suppressed and unsuppressed. I also prefer the aesthetics of the Colt compared with the raked look of the Glock guns.  None of my builds, incidentally, came near $1K.

Best investment I made for my 9mms AR was a Tubb .308 flat wire spring

I took the opposite route of most of the reccomendations. My glock mags were busy doing other things and I HATED how the angled-back mags look as compared to the Colt SMG mags.

My recommendation is anything with a magwell purpose-built for 9mm mags. If for no other reason than aesthetics. I also prefer the look AND function of a side-charging upper. Other than that not sure you can go wrong.

I've had extremely good service from QC10. Above and beyond service - they absolutely stand behind their stuff!  If you want a Glock lower I'd look at them first. They may be expensive, but the quality, service and help if you need it is simply outstanding. 

I've run a Colt SMG system (RRA 16" upper & lower w/Hahn block & metalform mags) for years with zero malfunctions, including flat nose bullets. LRHO is super easy to do in this platform. I run a non-dedicated top loader, so I can either run the std. latch and do easy swaps between uppers without LRHO or add a long finger bolt catch for LRHO although that 'captures' the block.

Just put another 9mm together with a PSA glock billet (non-LRHO) lower, hasn't run for long but runs fine with factory mags. So I can't say one is less reliable than the other. I do like the feed ramps that Hahns come with, and the 90 degree feed angle seems to be the more reliable setup overall.

The biggest difference I notice is that my colt smg set up does NOT like to seat on a full, or mostly full mag on a closed bolt. So LRHO is handy. Glock mags seat with no problem.

I do admit I prefer the look of the smg stick mag setup over the glock mags.