I was running about the wasteland collecting FO3's uniques when I went to go get The Terrible Shotgun. I had to double take when I got shells to put in it, as at 100 guns skill, it does a whopping 148 damage with slugs, the only other guns weapon that comes close to this is a fully modded Anti-Material Rifle with match grade ammo (145 damage on my char). I feel like this weapon needs to be scaled back slightly as it -is- a 20 gauge weapon that actually does more damage than all the 12g weapons. Even with the PPA mod (Powered Power Armor) and a mod that brings the DT of power armor much higher, on normal I can one shot T-45d wearers with chest shots with this thing non-sneak attacking (who have about 35 DT average).
Might I suggest scaling it back to be slightly under the riot shotgun in terms of performance (being a tooled up unique with supposedly much higher spread to compensate)