Alliant Techsystems stayed buoyant in its second quarter thanks to its commercial gun and ammo companies, but investors worry about future earning potential once the sporting group separates into an entity on its own. ATK’s sporting group — comprised of brands like Savage Arms, Federal Premium, Weaver Optics, Blackhawk, Bushnell, just to name a few —  bolstered a 26.4 percent increase in sales, up $111.1 …