As a fan of boomsticks I'm quite sad in base New Vegas shotguns are weak compared to other weapons in nearly every stage of the game (with one exception) because the dt system makes it so even if an enemy only has 3 dt after the penetration shotguns get through perks and ammo, it can still shave off 12-24 points of damage depending on what ammo type you use. When looking at the nexus I did not like any of the other mods that changed shotguns, because they either felt like they did too little or were too broken. So I decided to throw my ideas into the ring and booted up xedit. I have a list of the changes and my thought process behind each change. TL;DR all shotguns hit harder and are more accurate. 

DISCLAIMER
Though these buffs should help no matter what game state you use, I play on survival very hard with the mods "Better Damage Multipliers" and "Standardized Damage And Health". This may skew my perspective on balance from base vanilla New Vegas or those following the "Viva New Vegas" guide. But hopefully these help no matter what. Also I'm pretty sure this does not effect companion weapons (So just Cass). I also do not take "And Stay Back" as a perk because once you do, the game becomes way too easy and boring,

Caravan Shotgun
-Base Damage 45 > 60
-Spread 2.2 > 1.6

Sturdy Caravan Shotgun
-Base Damage 50 > 65
-Spread 4.0 > 1.5

For the Caravan Shotguns I wanted to make them better early game weapons, so I slightly increased their damage and majorly decreased their spread so you can actually hit what you aim at (imagine spending 99 cents for a gun with 4.0 spread).

Hunting Shotgun
-Base Damage 70> 90
-Base Spread 1.5 > 1.2

Just more damage and and accuracy, simple as. This is my favorite shotgun so I may be biased by increasing its damage by 20 while almost every other shotgun only a gets 12-15 damage buff. But I do not care I love pumping my gun too much.

Dinner Bell
-Base Damage 75 > 95
-Clip Size 5 > 7
-Spread 1.2 > 0.9
-Crit % Mult 1.0 > 1.4

So Dinner Bell in base game is worse then a fully upgraded hunting shotgun, doing 5 more dmg while being less accurate and holding 3 less shells in its tube while being one of the hardest weapons to obtain in the game. I decided to give it a tiny rework. It is still less accurate (with this mod, its accurate as a base game hunting shotgun with a choke) and holds less shells then a fully upgraded hunting shotgun, the difference is not nearly as drastic. I also gave it a 1.4 % crit multiplier, so it should give you about an extra 10% crit chance with an end game build. 

Single Shotgun
-Base Damage 50 > 70
-Base Spread 1.4 > 1.0

Pretty simple, makes the single shot you get count.

Lever Action Shotgun
-Base Damage 48 > 60
-Spread 1.9 > 1.6

Made it have the same damage and spread as the Caravan Shotgun, with the idea it is worse than the Sturdy Caravan Shotgun without cowboy and becomes better than it with the perk. 

Sawed-Off Shotgun
-Base Damage 100 > 110
-Base Spread 4.0 > 2.5

Just slightly increased its damage, while making sure you can actually hit something that's more then 2 feet in front of you.

Big Boomer
-Ammo Use 2 > 1
-Spread 3.5 > 2.5
-Projectile Count 14 > 7

I gave this weapon a small rework like the Dinner Bell to distinct it more from its standard version. Instead of shooting both shells at once it now shoots one at a time, so the projectile count was halved to reflect that. I did not change the damage of it, so this is a burst damage monster of a weapon. I do not know how strong this makes it, but the only way to get this weapon is to kill an innocent old grandma, and you would never do that would you?

Riot Shotgun 
- Base Damage 67 > 70
I decided not to change the Riot Shotgun too much, because even with all these changes to the other shotguns it is likely still one of the best weapons in the games with its huge dps, quick reload and big magazine size. I only changed its damage from 67 to 70 because I think 67 is an ugly number.