gaunt's ghost stuff, volpone blueblood colonel Gilbear.
their regiment, the Royal Volpone 50th, is considered as the most noble regiment on this side of the Imperium and so much more crap. Gilbear, like so many bastards of the Volpone, are aristocratic soldiers and they are too proud for their own good, but nonetheless, they can fight like deamons.
Designing him is not tough, just imagine any good fascist and you will get the look.
the hellgun is another thing. I have reference on the cadian kasrkin's but found it too rugged. So a more elegant breech and longer barrel would be good. And according to Abnett's books, the volpone have underslung grenade launcher fitted beneath the barrel, so it is also there. Using a mag filled with grenade rounds, the launcher is fired from the main trigger (possible to switch between lasbolts and grenade) with the front grip acting to cycle the grenade rounds, shotgun style.
Abnett also mentioned that they are heavy troops, which means segmented armour and helmets. The balaclava is for fighting in smoke-choke area.
Well, Gilbear is never a funny person but the scene that he was in is always funny. My favourite part is in the book Necropolis, where he and Gaunt's mission team was inside Asphodel's command center and the Zoicans are closing on them fast, 28 days later style. Gaunt decided to trust his scout Mkoll to pinpoint the target to the side of the structure but Gilbear insisted that they hit the middle instead. Gaunt argue that if he was proven wrong he will owe Gilbear a crate of wine, with Gilbear choosing the vintage at his liberty. But Gilbear pointed out that if Gaunt is wrong, they will all be dead. Gaunt simply replied him "Why the feth you think i bet?!" I swore I laughed till my side hurts.
And he have a hell of a long name.