Comparing weapons in Rage

Solution 1:

There are no player viewable weapon stats in RAGE. :( You will have to go by the description on the weapon and the ammo.

In general: Feltrite good vs. armor, explosives good vs. most everything.

Everything else basically comes down to "What is your preferred play style?", As most weapons have several ammo types you can use guns in various fashions to suit any situation and style.

Solution 2:

Double-barreled Shotgun, as the name hints, fires two buckshot shells in one trigger pull, as opposed to the combat shotgun's single shell firepower, therefore making it twice as dangerous in close encounters. It's the same ammo type, though.

The main difference is in practical usage: DBS has to be reloaded after each shot, whereas the combat shotgun with the magazine upgrade has longer lasting firepower, making it better suited for crowd control.