Actually there are quite a few players that have more experience with pistols than me as I haven't played with them since the dec release for I was disappointed how much they got nerfed. Still, the recent DEX bonus change didn't hit the (firearm) pistols as hard as it hit SMGs so I'd say compared to the rest of the light weapons, pistols are actually a viable choice now (Gunslinger got back to -3 AP). Only thing I wish would happen is dropping the STR requirement from Steadfast Aim to make Hammerer pistols a better choice than they are now. To me pistols are weapons that instead of relying on pure stopping power exploit enemy weaknesses (critical hits) and a critical damage pistol builds seem rather underwhelming nowdays. Wasting 3 STR only for that feat is too much, at least for the firearms.
Anyway, as for the recommended build I think the most important thing is to exactly plan ahead how many pistol shots will you be able to fit in. A smart, rapid 9mm Neo Luger is still the best choice. The 25 AP cost gets down to 20 with rapid reloader. Before the recent patch, with this pistol you could get down to 8 AP per shot @ 17 DEX (-48%) and Gunslinger (-2 AP). Now fastest is 9 AP @ 17 DEX (-36%) and Gunslinger (-3 AP). It's much better to aim for 10 AP @ 16 DEX as 9 AP won't give you a single extra shot (even if you take Point Shot and Rapid Fire into account). For the secondary weapon I'd recommend the amplified Electroshock Pistol because it gets down to 20 AP per shot @16 DEX (Gunslinger doesn't apply), so you will have easy time chosing the attacks as the AP cost can always be divided by 5 and you can use all of your available AP:
20 AP for Electroshock Pistol
10 AP for Neo Luger
15 AP for Rapid Fire or Execute (Neo Luger)
5 AP for Point Shot (Neo Luger)
10 AP for reloading (or 2 AP with the bullet strap belt so you can reload both weapons in one round for 4 AP. If you don't need to reload often it's better to equip the doctor belt instead.)
Remember that 16 DEX is earliest possible at level 22 (15 DEX + eel sandwich) so until this point it's probably a good idea to additionally carry a quick 7.62mm pistol. I'd actually recommend to stay at 15 DEX, rely on the eels for 16 and invest the last stat point in PER. At level 24 when you finally have 15 DEX, 6 AGI and 7 INT you will only have enough points for 9 PER. It doesn't matter though, Neo Luger has a 5% precission bonus and 10 PER would only be needed for Sharpshooter which is a poor choice here anyway. Neo Luger has weak criticals and you should try to make all your Aimed Shot special attacks with the Electroshock Pistol. To boost the critical damage you will take the Practical Physicist feat instead and craft the pistol with the circular wave amplifier.
Skillwise it should be pretty easy to distribute as you have plenty of points left even for high traps and throwing skill (Flashbang is great to open up for execute if you don't have enough AP for Electroshock Pistol).
For a firearms critical damage pistol build Steadfast Aim just doesn't seen to be worth it thanks to 6 STR requirement and only 0.5% increase for every base AP point. For a RR Hammerer it's just 12%. Not that great, and if you take Steadfast Aim can't have all - high DEX, 10 PER, and 7 INT. I'd dump INT in this case.
As an alternative you could entirely go for energy weapons as there is least resistance against it in the Underrail but now because of the DEX nerf you need whopping 17 DEX to fire the plasma pistol twice the round. But in order to keep Sprint go for : 6 STR, 15 DEX, 6 AGI, 6 PER, 7 INT and make use of Point Shot.
With Practical Physicist an amplified plasma pistol can do 500+ % of critical damage and Steadfast Aim gives you another 20% critchance so +crit googles are the better choice here, for firearms it's still the smart ones. For a secondary weapon it's probably best to take a laser pistol. It's still pretty quick to finish all the weak enemies (at 17 DEX you fire it for 5 times with 70 AP).
It could also pay off to dip into Psychokinesis PSI for free premeditated Electrokinesis stuns (great for Execute). One other useful PSI related feat would be Psychostatic Electricity to bump your critical chance even further. You can also craft and consume focus stims to get very, very high. I believe that you can get the critchance over 80% if you exploit everything you can. Still the question is how does it compares to other builds. DEX nerf was pretty heavy on plasma pistols. For 25 AP shots 14 DEX was enough, now you need 3 more. I hope to see Gunslinger working with energy and chemical pistols one day.
Still I think this build is very fun to play even if not the easiest one.
