It's cool to see the BR with a grenade launcher. It fills a hole in the UNSC arsenal. I also wonder what the UNSC uses for a squad support weapon (ie. Squad Automatic Weapon)?
Well the SA80 (L85) and G36 both have SIDE opening grenade launchers, but I have yet to see one that opens like a reverse M79 (or reverse revolver style).
I say that just leave that top space empty for someone to put an RIS rail themself, if you plan on making this into a pep model or whatever, I don't think anyone will want to fold a rail and fold the red dot.