Have you noticed that all of the tier 3 weapons are the most modern weapons? or even if they are old in design, they are remade with modern materials and style? To name a few....
A pump action, composite cross bow, with a trajectory drop 2X scope.
A synthetic framed, and all steel parts, 20 round drum magazine, automatic shotgun.
A 7.62X51 NATO automatic battle rifle, with ACOG(?) sights.
An industrial grade chainsaw, and a factory and battle ready made katana made of todays better and more refined steel.
A flamethrower that has a detachable fuel tank, for easier handeling and disposing.
What would fit with the gunslinger in this game, Is a modern revolver.
Taurus Ragging bull model 500.
A 5 shot revolver that fires the .500 S&W magnum. Has a hardend stainless steel frame, Rubber pad grips, and a muzzle break on it that is normally found on rifles to reduce atleast 60% of the recoil (although theres still quite abit of recoil on it, its just so its humanly managable)