In this post, I will try to cover the best shotgun ammo in Fallout: New Vegas. The shotgun weapon has the widest variety of them, especially 12 gauge shotgun shells. This can lead to confusion on which one to use and how to optimize the builds. So I will try to answer that

First, I will answer what you should use in different scenarios, this will clear up any confusion and you can start using optimized ammo. Generally, the important part is to understand Damage Threshold on enemies:

damage threshold vats fallout new vegas

As you see here, with perks and correct ammo, Deathclaw only has 3 DT, which means that my damage dealt is reduced by 3 per bullet.

So with a shotgun to maximize your damage you definitely need the Shotgun Surgeon perk. It gives -10 DT, making many of the enemy's fights much easier. Of course, if the enemy does not have any DT, this makes it much easier to combat them. So I will split answer categories based on enemy tiers of DT

0 DT enemies or 10DT + Shotgun Surgeon

For these enemies, normal 12 Gauge, Buckshot ammo is good enough with a Crit Average of 94.7.

However, if you want to maximize your damage, you should go for 12 Gauge, Coin Shot (114.7 - Crit Average), and 12 Gauge, Magnum (Crit Average - 108.9). The former is more costly to obtain so that explains its higher effectiveness.

12-15 DT enemies

These are usually Brotherhood of Steel Paladins and Deathclaws. The best options are 12 Gauge, Magnum (84.4 - Crit Average), and 12 Gauge, Coin Shot (83.9 - Crit Average, although with a higher sample it would probably surpass magnum)

Generally, the normal 12 gauge, Buckshot, is effective by itself (77.1 - Crit Average), making it a decent choice without super optimizing.

15+ DT

There are a few enemies in the game that have very high Damage thresholds. For this 12 Gauge, Flechette would probably work the best due to the huge reduction in DT. However, this would need more testing

General observations

It seems that shotgun critical damage works best with multiple pellets. So something like Slug ammo performs the worst

Going through the data

Here is the data that I observed. I used this equipment:

Riot Shotgun
Ulysse's Duster
1st Recon Berret
Lucky Shades

The result is 10 Luck and a fairly high critical chance.

Overall I tried to test between 10-15 shots to the Torso.

0 DT - Young Deathclaw testing

12 Gauge, Buckshot - normal ammo

Average Critical Damage - 94.7
Average Damage - 93.1

Type of damage	Damage
Crit	120
Crit	120
Crit	92
Normal	63
Crit	120
Crit	106
Crit	77
Crit	92
Crit	78
Crit	77
Crit	78
Crit	77
Crit	78
Crit	77
Crit	134
Crit	106
Crit	78
Crit	91
Crit	102
Crit	96

12 Gauge, 4/0 Buck

Performs similar to normal ammo

Average Critical Damage - 90
Average Damage - 88.5

Type of damage	Damage
Crit	78
Crit	91
Crit	106
Crit	78
Crit	77
Normal	63
Crit	78
Crit	92
Crit	105
Crit	92
Crit	106
Crit	92
Crit	91
Crit	106
Crit	78
Crit	77
Crit	92
Crit	91

12 Gauge, Coin Shot

Average Critical Damage - 114.7
Average Damage - 111.9

Type of damage	Damage
Crit	84
Crit	145
Crit	100
Crit	130
Crit	84
Crit	130
Crit	99
Crit	130
Crit	99
Crit	130
Crit	146
Normal	68
Crit	115
Crit	115
Crit	130
Crit	114
Crit	84

12 Gauge, Magnum

Average Critical Damage - 108.9
Average Damage - 104.4

Type of damage	Damage
Crit	115
Crit	114
Normal	69
Normal	69
Crit	114
Crit	100
Crit	130
Crit	99
Crit	130
Crit	99
Crit	84
Crit	84
Crit	130
Crit	130
Crit	100
Crit	130
Crit	99
Crit	84

12 Gauge, 4/0 Buck Magnum (handload)

Average Critical Damage - 91.6
Average Damage - 84.7

Type of damage	Damage
Crit	99
Normal	69
Crit	99
Normal	69
Crit	84
Crit	84
Crit	84
Crit	84
Crit	84
Crit	84
Normal	68
Crit	84
Normal	69
Crit	114
Normal	69
Crit	84
Crit	115
Normal	68
Crit	99
Crit	84

15 DT - Deathclaw testing

12 Gauge, Buckshot - normal ammo

Average Critical Damage - 77.1
Average Damage - 71.1

Type of damage	Damage
Crit	66
Crit	51
Crit	80
Crit	93
Crit	66
Crit	108
Crit	79
Crit	123
Crit	65
Crit	80
Crit	65
Normal	37
Normal	37
Normal	37
Crit	80
Crit	65
Crit	94
Crit	51
Crit	80
Crit	65

12 Gauge, Slug

Average Critical Damage - 60.75
Average Damage - 51.7

Type of damage	Damage
Normal	50
Normal	49
Crit	60
Normal	49
Normal	49
Normal	49
Normal	49
Normal	49
Crit	61
Normal	49
Normal	49
Normal	49
Normal	49
Normal	49
Crit	61
Normal	49
Normal	49
Crit	61

12 Gauge, Magnum

Average Critical Damage - 84.4
Average Damage - 82.8

Type of damage	Damage
Crit	69
Crit	99
Crit	99
Crit	98
Crit	69
Crit	99
Crit	98
Crit	84
Crit	68
Crit	68
Crit	84
Crit	83
Crit	69
Crit	83
Crit	115
Crit	68
Normal	53
Crit	83
Crit	84

12 Gauge, Coin Shot

Average Critical Damage - 83.9
Average Damage - 82.2

Type of damage	Damage
Crit	66
Crit	82
Crit	81
Crit	97
Crit	96
Crit	97
Crit	81
Crit	82
Crit	96
Crit	66
Crit	97
Crit	97
Crit	66
Crit	81
Crit	66
Crit	66
Crit	81
Crit	112
Normal	51

12 Gauge, 4/0 Buck

Average Critical Damage - 70.6
Average Damage - 64.7

Type of damage	Damage
Crit	77
Normal	48
Normal	49
Normal	48
Crit	91
Crit	62
Crit	91
Crit	63
Crit	62
Crit	63
Crit	62
Crit	63
Normal	48
Crit	63
Crit	90
Normal	49
Crit	76
Crit	63
Crit	62

12 Gauge, 4/0 Buck Magnum (handload)

Average Critical Damage - 79.9
Average Damage - 72.5

Type of damage	Damage
Normal	60
Normal	60
Crit	90
Crit	90
Normal	60
Crit	75
Crit	90
Crit	75
Crit	75
Normal	60
Crit	75
Crit	75
Crit	90
Normal	59
Normal	60
Normal	60
Crit	75
Crit	74
Crit	75

12 Gauge, Flechette

Average Critical Damage - 65.7
Average Damage - 63.7

Type of damage	Damage
Crit	59
Crit	58
Crit	68
Crit	69
Crit	58
Crit	80
Crit	68
Crit	59
Crit	58
Crit	58
Crit	58
Normal	47
Crit	59
Crit	79
Normal	47
Crit	69
Crit	80
Crit	79
Crit	58