To be fair, the Rifleman III only had ONE Prototype created, and it was destroyed in action in 2777. The wreckage was discovered by RotS archaeologists in 3146. Yes, the design Looks "Cool", as does the mini. I doubt the claim it took out NINE SLDF 'Mechs, unless it got a large number of LUCKY head hits, given the small amount of ammo it had. :-\ Only 2 tons of ammo (16 shots) for four Gauss rifles? That's less than 1 minute of combat. Better make those shots count!
Yes, it Thoroughly fills the role of "Rule of Cool". But to include it with designs that actually made it into production is giving it much more credit than it deserves. :-\
Granted, the XTRO: Gunslingers entry doesn't say "No construction information was found", simply that "Krupp has denied us access to their internal archives". (Whoever "Us" is. People from RotS, I guess?) Sadly, given that the RotS seemingly never took another look at it and put a "Riflemen III-B" into production (maybe using endo and more ammo), and Terra is now "Under New Management", I'm not sure TPTB could give us a new Production Model at this point. It seems that Krupp only has facilities on Terra and Mars. :-\
But, "Never Say Never!", and all that! :thumbsup: