Recently got a CMMG Banshee 5" pistol and was wondering if the upper would work with the Stern Defense 9MM Glock mag block and a run of the mill AR15 pistol lower.  I got some hints from checker333 when reading through ar15.com's version of "War and Peace" (https://www.ar15.com/forums/AR-15/Thoughts-on-the-CMMG-Guard-/15-713060/) and thought I'd give it a try.  Surprisingly, it worked great although I only shoot semi-auto since I don't have a full auto fun switch.

Here is a list of the big pieces.
--CMMG Banshee 5" RDB complete upper
--Anderson Arms AR15 pistol lower
--Stern Defense MAD-AD9 9MM Glock mag adapter
--H-2 buffer and carbine spring
--Glock and Magpul mags

Checker333 mentioned that the that the mag block would have to be lowered, so I filed an extra mag release so the Stern block would sit about .050" lower in the mag well.  I had to use a diamond file since my regular files would hardly scratch the metal on the mag release.   I also removed the Stern ejector since it interfered with the CMMG BCG and removed the Stern bullet guide to get rid of the nose up feed problems.  He also mentioned that he lost the LRBHO, so I tweaked the BHO lever a little by bending down the end that is pushed up by the mag follower.  So far, I've only tried it with some Glock 17 round and Magpul 21 round mags, but the combination has worked without problems with 115gr FMJ and 124gr Federal HST +P.

So if you're interested in trying this combo, here's one guy's way that worked (with props to check333 for providing the hints).  Now it's time to try get a CMMG RDB barrel/BCG kit to work with my SBR DDLES Glock small frame lower.  If it does, there's going to be some deals on the Equipment Exchange on 9MM regular blowback barrel and bolts.

The tools


The mag releases - modified on bottom


The block with guide and ejector removed


The finished setup

Good choice going with the CMMG RDB setup. Once you've tried it you'll wonder why you would bother with straight blowback in an AR platform

Anyway, have you considered the Endomag/Arc9 mag adapters for your standard lower? Same manual of arms as a regular AR, same pouches, reliable LRBHO. They work fantastic with the CMMG RDB uppers.

About your DDLES glock lower, if I'm not mistaken those are now the QC10 lowers aren't they? If so, all you'll need to do is remove the ejector from the lower and it should work fine with your CMMG upper. My QC10 lower has worked great with my CMMG RDB upper.

I have a RR lower. I started building a 5" radial delayed upper. I'm broke so I haven't finished yet. I originally planned on doing exactly what you did. I'm really hoping Stern or another company comes out with a magwell adapter that will work without modification.