Great comparison. What are those rifles called?
The upper is a well-farkled (optioned) AR15. The lower is the Kel Tec SU-16CA. I had an SU-16CA, it used PMAGs, USGIs, pretty much any M16/AR15/STANAG magazine you could find. The front “stock” folds out and becomes a bipod. The rear stock holds two more 10 round magazines. And the whole thing folds in half right behind the trigger assembly (folding disables operation).
Lightweight, accurate, reliable, and not scary at all. But operationally and effectively it was an AR15 in all but name only.
And it’s not an Evil Black Rifle... :)