It is interesting that neither the midlength nor the rifle length have slots at the rear.

Maybe it's to simplify manufacturing but since those slots help in cooling (it gets real hot at or near the chamber as I understand it), I would have thought it would be good to have them all the way back.

Then again, these are prototypes.

I've definitely changed my mind about the 'dissy with a MOE'. As Aragorn says, it would be great as a general purpose beater/trunk gun, especially with a pencil barrel.