Andy:
Thank you!
I just got of the phone with Atomic Engraving in LA. They made my lower.
Same answer.

Just because I wanted to get another pistol started, I started ordering parts today.
I can then do tryouts on what works and what does not work.

What buffer weight and spring strength do you run or recommend?

My CMMG is running factory standard spring and buffer. What ever came with the lower. And I made a spacer. Mostly just to shorten bolt travel.
The Black Creak is running a Tubbs flat wire spring for a .308. And a Vltor A5H4, 6.8 oz buffer.
But honestly I put those in because that's what all the cool kids were doing. Now I kinda think factory weight is probably just fine.
Both these guns are un-suppressed 14.7ish barrels.

My ejector wiggles, its in a mag block. But works fine.
Pistol tube and 9mm carrier
Block and carrier are starlos upper is a standard flat top.

Why didn't you just go with a regular 9MM dedicated AR lower? I got mine form REHV Arms.
Probably would have solved all your problems for the start.

At the time was looking for lowers, i just couldn't find a dedicated colt lower with short mag well cutout.
Plus, manufacturing your own lower was something i wanted to try too. I ended up getting my lower as a group buy from Atomic with a great discount.
That's the whole story behind it.
Looking at it now, I see it as a learning curve and maybe should have considered buying something different.

I'll give REHV Arms a look later today. Got to build another one too...

Thank you!

Scorpion

Was not trying to be a douche bag about your Fire Arms endeavors. Sometimes I wonder if the Juice is worth the squeeze with some of these scratch builds that's all. Good luck and hope that you are able to get your 9MM project working without too much frustration.

G'day folks!
Thought I share an update and the final results:
It definitely is the upper causing the problems.

1. The ejector claw is supposed to wiggle. Bending the arm slightly to the center axis of the BCG is desired and while it may look silly-it works. Perfect ejections every round.

2. The BCG of Kaw Valley and the Matrix Arms Upper do not work together. Kaw BCG will extract the rounds further to the back causing the case to eject to the 3-4h position. As the Matrix Arms cutout is at the most forward position with approx 1.5in opening length-the cause for the FTE problems was quickly discovered after comparing it with a slick side upper. The cutout there is about 2.8in in length.

3. Matrix Arms appears to have a dedicated BCG for their uppers. I am looking into getting this BCG for my upcoming build. I am not sure how this is supposed to work, because the ejection is triggered by the ejection claw and not the BCG. Lets see...

4. With the new slick side upper attached the next question was the buffer weight... I started with a 6oz but that lead to significant problems. Plus the recoil was not pleasant. A 7.5oz buffer and heavy spring seemed to work significantly better. Recoil was much more reasonable. Final test was run with a 10.5oz buffer and a 308 spring. I liked this setup best. nice low recoil force , good control and the brass clears the port very well.

5. Feed Ramp and Magazines. First off, the ramp must be secured with the allen screw and loctite. And it better be aligned correctly. On a Colt lower the magazines are the key. Unfortunately the metalform mags are the best and come in at $28/piece. The PSA mags are perfect too and are currently on sale in store only. Luckily I have a source to ship them to me. The ASC Mags do not seem to work at all. The feed lip is completely off and cause havoc with the bullets.

6. Gas Blowback: I am a left-handed shooter, hence the idea of the side charging upper to prevent any gas hitting my face. So far the slick side upper and the PSA Ambi Charging Handle work very well. Minimal gas discharge in my face.

7: Range Test: Round Nose 115gn Federal and handloaded JHP 115gn was used. 147gn Hush tried later. Round Nose works flawlessly while the JHP seem to dislike the feed ramp angle. I used Everglades Ammo JHP and Nosler JHPBT. The EvergladesAmmo JHP worked better as the tip is not as curved vs the Nosler.
147gn Hush was a thing of beauty. Zero problems. But they are expensive...OMG!!

8: Conclusion: For anyone wanting to build a dedicated 9mm Colt Setup: It works, I looks like a 21st Century interpretation of a Tommy Gun. Costs in my case totaled at around $700 for the entire build. Not counting the additional experimental parts needed. Since I do not own a Glock it made no sense to jump on the Glock waggon. I have put approx 250rounds downrange and after the mods and rework it worked flawlessly.
As to the 80% lower and manufacturing it, it is messy and loud. the process takes about 60min and the outcome was perfect. It all breaks down to what type of jig you use. Quality is key...

Thank you all for your help support and motivation! Feel free to comment and fire away!

Matt

That's a heck of a summary, Matt. Thanks!

My understanding is that the PSA mags are made by Metalform.