I'm in this group and know the gun and guy who made it.
It is a 300BLK AR with no gas port/block. The gun is a manually-operated, single-shot side-charger. He used a side-charging upper/BCG and cut the rear of the BCG off so the buffer tube isn't needed.
Those are old pics, I'll see if I can get newer ones. I don't think the gun qualifies for Hall-of-Shame, it really is a decent little gun.
EDIT: here is an updated pic:
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