How do the weapons and ammo introduced by update 27 and 31 (Gage Sniper, Shotgun Pack DLCs) work?

Update 27 with the Gage Sniper Pack DLC introduces new bolt action sniper rifles. Its website describes them as:

...if you are a good shot, one-shot-one-kill may actually translate to one-shot-three-kills. because a bullet fired from these rifles will happily keep travelling through several "targets" - if they're soft enough - before it comes to a halt.

Update 31 with the Gage Shotgun Pack DLC introduces Flechette ("long range armor piercing"), AP Slug shotgun ammunition ("penetrates body armor, enemies, shields and walls") and HE Rounds (explosive rounds).

What are the mechanics behind those weapons and ammunition? Which targets can a sniper rifle bullet or AP Slug or Flechette shotgun ammunition pass through? Is there damage reduction?

Also, how do those weapons or ammo work on objects that other weapons' projectiles can't pass through (i.e. Bulldozer's faceplate, Shield unit's shield, Maximum Force Responder's [tan cop] body armor)? Do those items reduce the damage of AP ammunition passing through them?

Solution 1:

              Health   Headshot multiplier
Security        30      3.00
GenSec          50      5.00
Cop             30      3.00
FBI             50      5.00
Swat            80      4.00
Heavy Swat      100     1.67
FBI Swat        130     3.25
FBI Heavy Swat  200     2.00
Sniper          40      2.00
Shield          100     1.67
Taser           360     1.80
Bulldozer       5500    22.92
Gangster        40      4.00
Biker           80      4.00
Cloaker         320     5.33

To use this information combined with the weapon damage:

[Rattlesnake][1] : 130 base damage. 
[R93][2] : 250 base damage.
[Thanatos .50 cal][3] : 2880 base damage. 

An unaware enemy will always be a one-shot kill though.

I couldn't find any information regarding body armor or bullet slowing factors, but i'm guessing that if you take the Thanatos .50 cal (for example) which has a base damage of 2880 and you have lets say a straight row of security guys (30 health each) you are able to shoot through 96 security guards with one bullet. My assumption is that by each enemy hit the base damage of the weapon degrades regarding how much health the enemy has.

Another example would be if you shoot a bulldozer in the body (again with the Thanatos). Thats 5500 - 2880 = 2620. If you shoot him a second time and there happens to be an FBI heavy swat standing behind him. Thats 2620 - 2880 = -260 (an FBI heavy swat having 200 health would also die).

Solution 2:

With sniper rifles and AP slug ammo, you can shoot through Shield units' shield, enemy bodies and walls. In the game's files, weapons and ammunition with this ability have the can_shoot_through_shield, can_shoot_through_enemy and can_shoot_through_wall variables all set to true.

Flechette rounds do not penetrate Shield units' shield and can't shoot through enemy bodies and walls (they don't have the above-mentioned variables set to true). They can only penetrate armor (e.g. tan cop body armor). Penetration of armors do not reduce the damage (unlike how AP slug rounds work with shields - see below).

Bullets penetrating shields deal only 25% of their damage, provided the weapon is capable of that (sniper rifles, shotgun AP slug ammunition). Penetration of walls and enemies do not reduce the damage.

^{More info at: The Long Guide - Weapon Stats - Advanced Concepts - Penetration of objects and enemies by Frankelstner.}

From Shotgun Mechanics post-DLC by KarateF22:

Shotguns did not receive any changes to their core mechanics outside those imparted when switching ammunition. There is still a max damage range and then a zero damage range beyond that, between the two there is linear falloff of the damage. I will attempt to explain how ammunition effects the shotguns.

• 000 Buckshot are the most simplistic, they simply cut your ammo supply and decrease your average ammo pickup amount by 30%, which can occasionally have no effect or more effect than expected due to rounding.

• Flechette Rounds increase the distance between the zero damage and max damage range by 35%, decrease your average ammo pickup by 30%, and reduce damage. They will pierce Tan Cop armor but seeing as hitting armor means you missed their head this is useless. Honestly the Flechette rounds are terrible and you shouldn't use them.

• Slug Rounds removes the multiple pellets of the Shotgun and turns it into a single bullet. Despite this, it experiences normal Shotgun falloff with no range extension (this is incredibly unrealistic, usually Slugs have as much or more range than Flechette). You gain the ability to pierce shields and punch through walls. Your average ammo pickup is decreased by 50%, which is usually very noticeable.

• HE / Frag Rounds increase the distance between the max and zero damage range by 250%, but it does not experience damage falloff. For example, the Loco goes from max damage at 8 meters to zero at 20 meters normally, with the frag round this would be max damage up to 38 meters, at which point the bullet disappears. They also have the most severe pickup penalty, at 60%, which is enough to sometimes get 0 ammo from pickups. Frag rounds cannot head shot, but completely stun any unit other than the Cloaker that is struck by them as if they were struck by a grenade. You can stun-lock a Bulldozer by firing Frag rounds at it repeatedly over time. The big thing to take away from this is that while Frags are useful for stunning specials and other units, they are very subpar at actually killing.

General mechanics of explosives:

• They do not benefit from headshots.
• Shotgun HE rounds benefit from all damage skills except Cleaner basic. The other explosives benefit from Spotter basic only and nothing else. Even though HE rounds benefit from Overkill basic, they do not activate it on their own, because the Overkill skill (basic or aced) is only ever activated when enemies take bullet damage.
• Explosives may damage Bulldozers several times. Bulldozers have armor on their back, chest, stomach, neck, throat and their visors. The explosion deals full damage to the Bulldozer for each piece of armor in the explosion radius plus its original damage. Due to that, Bulldozers take 7 times as much damage when their armor is still intact (the second visor can take damage only after the first one is broken). The armor pieces (except for the visors) have only 80 hitpoints however, after which they simply fall off. Thus Bulldozers take much less damage from explosives after their armor is broken.
• Some enemies have a slight resistance to explosions, so the final damage is multiplied by the following numbers:
  • GenSec Elite/Murkywater: 0.8
  • Heavy SWAT: 0.9
  • Tan: 0.9

^{Source: The Long Guide - Weapon Stats by Frankelstner}