One of my favorite parts of the books is how they emphasize that Elkoss Combine specializes in making cheap, fragile, shitty knock offs of proven designs. I originally had Tanya use a Tempest SMG because it's a bullet hose that requires little accuracy (she's not the best shot, she can pass Alliance marine standards but that's about it) before I thought it would make sense for her to have an easier to control rifle that made it past shotgun range. 

Oh, note about shotguns for anyone unfamiliar with them in real life; they are absolutely devastating past 50 meters (and way further with slugs). You don't actually have to get close enough to French kiss somebody to hurt them. Consider people have been hunting with shotguns for well over 100 years, and animals don't tend to stick around when they notice you, it's pretty safe to assume you have a bit of leeway for range. :P