Sorry this is going to be a very long post because this build pique my interest. I'm actually playing this exact build on dominating right now, with DC and expedition content untouched but done pretty much everything else.
First my build:
http://underrail.info.tm/build/?HgUFCwMNAwbCoEoPAADCoFMAAAAAfMKLMFp6AC1GRgAAUCs5wqMiwrAqJkcewo_ClsKYSzHCkMKkwrHCpeKnvgrit7AF378Why 5 STR and not 7 STR?
I'm not using shotgun burst and I'm not getting Full-auto. 5 STR so I could use Vindicator shotgun
Why 5 DEX and not 6 DEX for Grenadier?
I suppose you could lower PER to 12 and drop a feat of your choice to get Grenadier. This is personal preference really. While playing my build I rarely have the chance or the need to use the same type of grenade twice. The battle is already over before grenade cooldown come into play.
Why AGI at 13? What's the point?
You need every last bit of MP to shell everyone in the face. Expert Sprint = 10 extra AP which is always useful for either an extra shell or an extra psi CC or pop medicine at 10 AP since I'm using bolt Quiver.
Con 3? Die a lot? Reload often?
Not really, I do die quite a few time to Death Stalkers but I considered that a given. Sometimes I do die when I play just a bit too aggressively (avoidable if I played it safe but I'm impatient sometimes). But I played the game so many times I would say I'm a veteran player. I will admit this is a glass cannon and newbie unfriendly build. If you want to use my build for your first run please play at normal or below and be prepare to abuse the reload button.
Psi hybrid at WIL 3?
That's fine as most of the psi abilities are use for crowd control (CC) and not for damage. ThermoD gets the job done at WIL 3 with only 70 base Metathermics along with shotgun shell damage.
Gear
Vindicator shotgun (short barrel, forward grip)
note: long barrel offer less damage + higher precision + narrower spread angle, not worth it because precision is great when you shell someone in the face at near melee range even when using short barrel. A wider spread angle is not a bad thing because that means more enemies are now under your shotgun's cone of fire. Shotgun Tube Extension - not bad but not great. Shotgun Choke = bad due to the exact same reasons as long barrel. Forward grip = great for non-combat shotgun as it lower 5AP per shot
Not using combat shotgun?
I'll explain this in more details below.
Scoped Pneumatic Cyclon Crossbow
Bolt Quiver
Infused Rathound Leather armor (mid ~ end game +11% crit chance)
Seeker googles (mid ~ end game, +18% or more crit chance, depends on your luck on component RNG roll)
Infused cave hopper tabi
On Dominating the first 9 level or so is a struggle because I couldn't afford a shotgun. For early game, Temporal distortion/grenade/SMG single shot will be your main damage output. This build really starts to get strong once you have enough money for a proper shotgun + ammo. At mid ~ late game it'll be one shot - one kill/multiple kills.
Why versatility?
Versatility is most effective when you can combine chem pistols w/ some other class (incendiary pistol for 2 turn fear, acid pistol for entanglement, Cooked shot ignore evasion and is AOE). However, my build doesn't have enough ability points for DEX to use chem pistols effectively. Crossbow is a great choice w/ shotgun for 1 turn stun using Shock bolt (MKIII) with no cooldown, and incapacitation using tranquilizer darts. Incendiary bolt seems great on paper but in my experience the fire and its fear effect doesn't proc often enough to justify the lost utility slot.
I took 15 base Crossbow skill for Marksman. Around mid game I was able to fire my crossbow @14 AP (Scoped Pneumatic Cyclon Crossbow, bolt quiver) - you don't really care about crossbow damage; you just want the special bolt to hit using as little AP as possible.
Psi setup explanation:
0 Thought Control - WIL is too low to use TC
45 Psychokinesis - Force Field, Electrokinesis, Disruptive Field, Electrokinetic Imprint are all important CC skills
70 Metathermics - Cryokinesis extreme range sniping + incendiary grenade area denial is a lifesaver early game (you'll eventually abandon this tactic once you have a proper shotgun). Cryostasis is a very important CC skill because it's silent and works on enemy under second wind (stun immune). Thermodynamic Destabilization (ThermoD) is one of my main damage dealer, more on this later. Cryo-shield is very good against melee (annoying dogs, pit bulls, crawlers, death crawlers, knifers) and can put out the fire when you are burning. Exothermic Aura is pretty much mandatory against expedition spiders. My shotgun build need every last bit of mobility and you can't afford to be webbed (immune to webbed for 4 turns).
70 Temporal Manipulation - LTI and Psycho-temporal Contraction (PTC) is pretty standard and require no explanation. Stasis is a great CC, offensive and defensive skill all in one. You can use Stasis to take one enemy out of the fight for 2 turns. You can Stasis an enemy w/ Pseudo-spatial Projection (PSP) and strip it of PSP while it's under stasis. You can net/EMP a stasis enemy (95% chance too regardless of target's evasion provided you have high enough effective throwing). PTC lasts 2 turns and adrenaline shot lasts 3 turns. On the turn when PTC is about to expire you can use every last bit of AP until you have 15 AP left, Stasis yourself, wait 2 turns and extend your max AP by another turn. The enemies are usually group around you for a convenience ThermoD finish too. Important skill/psi ability is on cooldown and can't be use? LTI + Stasis. What I'm trying to say is Stasis is worth it for the extra 15 skill points investment.
Why Kneecap shot?
Mostly for use around early ~ mid game when your shotgun shot isn't powerful enough yet for 1 shot = 1 kill without the powerup from Sixth Shot. Shock bolt + melee range Kneecap shot = 1 dead enemy standing. Late game you can use this to kite tough melee enemy (Balor, any sledgehammer npc using metal armor, Burrower warrior, etc.), allowing you to ignore them while you concentrate on other enemies.
Comments on Shotgun feats:
Sixth Shot is the most powerful shotgun feats, period. With max specialization your sixth shot now gain 200% BONUS damage on top of the original, usually critical damage
Why take Barrel Stare and Leading Shot together? Aren't they mutually exclusive?
No they are not. At least for my build it's not. Barrel Stare is to ensure a shotgun shell to the face at melee range is lethal. Leading Shot is use to deal w/ high evasion enemies and to help trigger ThermoD.
Why no burst feat like Full Auto?
You don't need to use burst. Combat Shotgun burst = 50AP and while it does delete enemies it's not really AP efficient. One single 20p Shotgun Shell shot from a Vindicator shotgun (short barrel, forward grip) is like a mini burst at mid range and only cost 20AP. At close to melee range one shell is usually enough to delete a single target provided you choose the correct shell loadout.
What's the correct shell loadout?
20p is the prefer shell choice because each individual pellet has its own chance to hit and crit. More pellet = more chance to hit/crit. Also Vindicator is the shotgun with the lowest min damage and highest max damage. More pellet = higher chance of at least one pellet reaching max damage. 20p is weak against heavily armor target (read: high mech resist, mech threshold is usually not a problem when you have high crit chance + bonus crit damage).
12p is my least favorite ammo as it fire less pellets than 20p while doesn't really offer any significant advantage.
6p is my prefer choice of ammo against heavily armor target because 1. you can buy this in bulk 2. It ignore 30% of mech damage resist which is usually good enough already. 3. it fires more pellet than 3p, see above on why more pellet = better.
3p does have its use but it's rare, expensive, and heavy. It can proc daze (1st shot), and stun (2nd shot on dazed target) but I rarely use them. You should use this against the final boss tho as it ignore 50% mech resist.
Update: now that I've tackle expedition, you should use 3p against crabs and strongman.
Math-wise you can see the damage difference too:
20p = 20 pellets * 6% shotgun damage = 120% shotgun damage
12p = 12 pellets * 9% shotgun damage = 108% shotgun damage
6p = 6 pellets * 15% shotgun damage = 90% shotgun damage
3p = 3 pellets * 25% shotgun damage = 75% shotgun damage
Of course this is only referencing the raw damage before mech threshold/resist calculation but it's also an important data point to consider.
As a side note my build can also use leper poison/corrosive acid bolt to lower a target's mech resist.
Fragmented Chaos - great, must have for all shotgun build along w/ Sixth Shot
Pellet Mayhem - very good feat because you must remember each pellets has its own individual chance to crit. When using 20p shell you'll notice your crit chance directly translate to number of pellets criting. This is also why Body horror is actually a good feat for 3 WIL shotgun build.
Perfect Scattering - absolutely useless in my opinion. Even at 2 points of damage using 20P shell that's only 40 extra damage. Even if it's add to the base damage, which I'm not sure it's, w/ a crit chance of say, 50%, and a crit damage bonus of say, 175% and at sixth shell (200% bonus damage) the extra damage is only (20+20*275%)300% = 225 damage for a precious feat slot. Worst case scenario: 3p, 1 points of damage per pellet, no sixth shot bonus = (2+1*275%) = 5 extra damage. There are many other better feats out there. I would recommend avoiding it.
How to use:
I have around 47% critical chance (from gear) starting from mid game without using any food or drugs. Hardcore chip +5% crit chance. Body horror +3% crit chance. Focus stim +15% crit chance. Total crit chance = 70% + (3% ~ 12% from pellet mayhem). My first shell to the face using 20p usually deal around 400 damage (after mech threshold/resist/miss calculations) to a target. Once Six Shell buff is up I have seen as high as 1.7k damage. You see a crowd, thermoD, stand 4 tiles away from the target (with 3 tile of empty space between you and the target. You can check and see you need 30MP to move and stand besides the target). 1 or 2 shotgun shells should blow up the target. Follow up w/ grenade if required. This build has shit load of psi CC options so you do need to watch out and manage your psi pool. Stasis + Force Field are your panic buttons. Abuse line of sight. You can trigger a mini burst per shell when you stand 1 tile away from your closest target but you'll lose the barrel stare bonus. I find this build is pretty strong and perform the same, if not better, than my 5AP per punch psi-monk build. Only my pure psi builds are undeniably stronger than this build.
