I think the RRG might be a Fallout play on the Type 87 35mm Grenade Launcher.
I dunno man those glittering trogg things look like they have a good amount of armor.
I was thinking about the Bloodmen but yeah, I always bring something with serious penetration, for Deathclaw encounters or heavy Legion and NCR squads. It's just a good policy to carry a lot of gear with a lot of different damage rates.
Although in my case i'll just use the 155 DAM Superheated Saturnite Power Fist against those Gehennas.