In most first person shooters, shotguns are powerful close ranged weapons that are better than melee weapons due to their viability at slightly longer ranges.  New Vegas's shotguns are just short of useless except at point blank range in which melee and unarmed weapons outclassed them.  I hated this.  Aside from a couple of unique shotguns and the riot shotgun, these weapons were underwhelming at all points of the game.  I decided to make my own personal changes to solve this problem.

The mod works by adding new modifiers to ammunition and changing a couple of existing ones.  All shotguns now have MUCH higher accuracy and a slight DT shred.  This results in shotguns being more powerful at mid-range, serving similar purpose to the lever-action rifles but also remaining unique in the fact that they aren't nearly as good for sniping, even with slugs.

Features:

• More accuracy on all shotguns.  No longer will your buckshot fail you when trying to shoot someone arm's distance from you!
• Slugs have more kick.  They do significantly more damage and are much more accurate.  They still are balanced as they aren't as accurate as rifles.
• Compatible with most mods.  This only modifies the ammo, so any mods that add weapons that use the 12 or 20 gauge ammo will get the bonuses!
• Works with all the DLC, including Gun Runner's Arsenal and the preorder packs.  
  

I personally use a lot of "realistic damage" mods and this mod is balanced around that.  This may or may not be balanced in the vanilla game.

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Changes (Updated 8/22/13):

All non-slug:  Spread multiplier of .50 (50% increase in accuracy)
12 & 20 gauge buckshot:  Added -3 DT
All slugs:  Spread multiplier of .05, a damage multiplier of 1.5, and -5 DT 1.4 and a DT shred of -2.
All Magnum:  Added -2 DT on top of the existing -3 DT, damage and CND penalty remain
12 gauge beanbag:  Increased fatigue damage from 250 to 450 as suggested by angryglock, I removed the changes to beanbag ammo to avoid conflicts with bugfix mods that change the scripts related to the ammo itself.  This includes the accuracy buff that originally both buckshot and beanbag were to use.  It will remain this way till I find a workaround.
12 gauge coinshot:  A damage multiplier of 2x! but a CND penalty of 1.75.  The "VanillaCoinShot" .esp makes it identical to the magnum, just like the vanilla game.

GRA Changes:

Pulse Slugs:  Same accuracy and DT bonuses as the regular slugs.  Damage not changed.
Dragon's Breath:  Only added the accuracy buff.
Flechette:  Added accuracy buff and extra DT shred.
3/0 and 4/0:  Gave normal accuracy and DT bonuses.

Upcoming Features (possibly):
Coinshot, flechette, and Dragon's Breath ammo for 20 gauges (including the proper leveled/loot/vendor lists) IN BETA RIGHT NOW
A perk that can be taken to increase critical damage/chance at closer ranges

Requirements:
A copy of Fallout: New Vegas and a know how on how to install and manage your mods and load order.  The GRA version obviously requires Gun Runner's Arsenal.

Installation:
Drop one of the .ESPs into your data folder OR let Nexus Mod Manager do that for you.  Select only 1 .esp, not both.

Compatibility:
This mod should be compatible with most weapon mods.  Any mods that add weapons that do not use 12 gauge or 20 gauge ammunition will not revceive the bonuses that other shotguns get.  Any mods that modify the 12 gauge or 20 gauge ammunition or overhaul the ammo system (CaliberX) will likely not be compatible with this mod. Edit:  angryglock has informed me that the changes to beanbag ammo causes conflicts with YUP and MM.  Any version older than 1.1 will cause conflicts with these mods as they change scripts related to the beanbag ammo.  As of 1.1, changes to beanbag ammo have been removed.

Requests:
I may accept requests for balance changes.  Compatibility patches aren't going to be made I might make changes to my mod every know and then to reduce the number of possible conflicts this mod may have; however, full fledged compatibility patches are HIGHLY unlikely.  New features are likely to not be accepted unless I REALLY like it AND I don't feel too lazy to implement it.

Notes:
This is my first mod so please tell me if there are ANY bugs, I am next to clueless on this stuff.
I spent way too much time on these simple little changes in the G.E.C.K.

Tools Used:
Nexus Mod Manager
Fallout: New Vegas G.E.C.K.
FNVEdit

Patch Notes:

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8-22-14 V1.2b - BETA Version
-Added 3 new ammo types:  20ga Dragon's Breath, 20ga Flechette, and 20ga Coin Shot.  NOT IN LOOT/LEVEL LISTS, MUST SPAWN USING CONSOLE COMMANDS
-Coin Shot now has a DT multiplier of 1.5 to counterbalance the massive damage it gives.  For comparison, hollow point ammo has a DT multiplier of 2.0.

THE IDs FOR THE NEW AMMO ARE:
20ga Coin Shot:  xx001658
20ga Flechette:  xx001937
20ga Dragon's Breath:  xx001938

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8-21-14 V1.1 - UPDATE
-Slugs damage multiplier changed from 1.5 to 1.4, slugs DT shred changed from -5 to -2, fixed slugs not having the right accuracy multiplier
-Beanbag changed REMOVED
-Added GRA version

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8-20-14 V1.0 - Original upload