So there's this neat form of Storm Trooper in the Star Wars universe called a Dark Trooper, which is kinda hard to find any solid unified info on, but I found that the Phase 3 dark troopers were really neat and the Inquisitorium Dark Troopers were huge and carried massive weapons.
The idea stems from "What if the First Order in the new Star Wars series began developing Dark Troopers?" Their weapons had to be big and powerful enough to take apart armor and defensive emplacements.
I'm not sure how well this would fit in the Star Wars universe, but hey I did my best
I do not own Star Wars or have the rights to any intellectual property involving it, this is just fan based concept art.
Edit: Made some minor changes to Concept 5, after hearing suggestions from others. It now includes a more obvious barrel Shroud, and a few bits and pieces here and there that aren't really worth mentioning...