I am level 25, on Hard mode, and have found that I have a very hard time killing most bad guys of similar level. I have a rare shotgun w/ exploding ammo that does 70 base dmg and it's my best weapon, but even still takes a good 10 shots to kill most robots or super mutants.
Last night I stumbled upon a .50 Cal Hunting Rifle, which I decided to pick up as I hadn't seen one before. It does 90 damage and has some mods for scope, fast reload, etc. I figured shotgun up close for 70 dmg + 15 dmg per exploding bullet would surely be comparable to the 90 damage .50 Cal, but to my surprise the Hunting Rifle does almost 5-6x the damage of any of my other 70 damage shotguns or 70 damage rare rifles (.308, .38, .45, laser). It kills most super mutants in 2 hits, raiders in 1-2, even level 30-35 enemies die in 3-4 shots.
Why does it do so much more damage? It isn't rare and has no special stats. I would think that going from 70 to 90 damage would be just over a 28% increase, but it seems more like 500%. I just want to understand why.