https://underrail.info/build/?HgsDAwUOAwc8wqBtAAAAAFA_SzIAdWoIN0wAAHNGABQ8OyZNw50VT8OfSsOhCCrCh8OiwprCtcKFKSvCnsKd4qe0CuK_hgXfvA
Another theorycrafted build, this time to make LMG/Miniguns comparable to their AR overlords. Not playtested.
So, the main payoff for LMG/AR is
Concentrated Fire, right? To maximize the damage of Concentrated Fire, you need 95% accuracy, or as close you can get to it. But while ARs can run ambush to halve evasion, LMG/Miniguns need to be 95% armor penalty tincans for
Heavy Metal, the main payoff that is unique for them.
However, Heavy Metal is indeed a strong payoff. As are Ratchets with +6 (with Full Auto, +8 with Muzzle Brake, +10 with MagDump) Bullet Bursts with Expertise at 25 AP only. So lets start looking at the solutions.
Accuracy: For an LMG burst to instagib a target, you need this as high as you can. Without ambush or shell shock; you're limited to as high of a perception you can manage.
Fortunately,
Brute Aim is truly brutal in this aspect, allowing you to hit very high perception values as long as you don't need many points in other stats. 16(+3) is your baseline, +1 from Juice, +1-3 from Food, +2/+2 from Supersoldier Drug and Bioluminous Marsh Honey for really difficult fights. If you're popping them all, you can freely use Iron Head for ~45% damage boost from Heavy Metal +5 since you're actually overcapped on +PER (11, max 10). Insane damage; if you need more, use Miniguns over LMGs (typically vs bosses,
12.7mm Contaminated Bullets).
Overkill: Playtesting this build (using CE on a lategame save) makes this issue, pointed out by commentator below, very pressing. LMGs with Concentrated Fire +10, Heavy Metal +5 and 16 PER (+3 from Brute Aim) is absolutely overkill for single target damage. Even bosses, assuming you're using 12.7mm Contaminated Bullet Miniguns.
My solution is the
Fusion Cannon. There's already a lot of overlap in a Fusion Cannon build and a Minigun build; so making some changes to the build to make the Fusion Cannon a viable secondary weapon is the main way this build is distinct from AR builds. While AR builds do have Grenade Launchers, they aren't as damaging without Demolition Man, and even with Demolition Man, Fusion Cannon is an absolute force of nature with Heavy Metal +5.
The updated build reflects that. What I replaced was Gun Nut and Decomissioner; Gun Nut is simply not necessary with the overkill single target damage of LMGs and Miniguns with that high perception, neither was Decomissioner, even vs Nagas. The MG3-42 is a very viable alternative to a custom Ratchet (especially as it uses the common 7.62 ammo), further lowering value of Gun Nut.
In exchange,
Tricky Trajectory and
High Technicalities come in, at L22 and L24. Tricky Trajectory is very powerful, mostly because it lowers evasion on top of the damage; and High Technicalities with 7 (+2) INT is a very good feat to take even for a secondary weapon (+16-32% damage). Its not worth it to specialize in HT without 10+ INT, so you still specialize in Concentrated Fire levels 20-30, allowing you to oneshot bosses with LMGs/Miniguns, and Mobs with TNT + Fusion Cannon. Be sure to keep a stealth armor set to set up TNT lure, then quickly swap back to your 95% Armor Penalty set as the enemies start grouping up.
Survivality: This is the main issue compared to ARs. ARs can plink off 4+ targets instead of 3 per turn because commando and rapid reloader, and move behind cover afterwards. And do it from a longer range compared to Heavy Guns.
My solution is drugs. Namely,
Morphine. Morphine + Aegis + Conditioning is 75% DR from the most common damage sources,
switch to Balor's Hammer before you end turn for +20% Mech DR from Heavy Metal. Use Lifting Belt or eat Canned Meat before the fight for 100% Mech DR for 3 turns. The heavy armor should protect somewhat from other damage types. Lategame, All-In + Supersoldier Drug also reaches 100%, as does 13 STR Minigun Heavy Metal, Supersoldier Drug and Lifting Belt + Canned Meat; if you want Minigun + Fusion Cannon for whatever reason.
Use a blast cloth tabi/balaclava if needed. Energy Shield (High/High) is good vs energy and electrical attacks. And, of course,
Bullheads. You need a lot of them. If you hate fishing with 3 DEX, get Merchant Refresh and stock up on Demon Squids from Al Fabet. Easier fights don't need this much of course; a Flashbang is enough.
Economy: The last hurdle. I offer two solutions.
One,
Metathermics for the really trash mobs. Thermo Destabilization is good even in big fights; but tears smaller ones apart, especially with a grenade or two.
Two,
Disassemble. Disassemble is very strong for Heavy Gun builds because Fusion Cannon; even if you're not building around it, Heavy Metal + high PER is often good enough. Disassemble at 2nd level + Pickpocketing should theoretically give enough money to keep your ammo belts filled. Or to craft your stuff in time, especially your first LMG and your first set of Heavy Armor for Heavy Metal.
In the really tough fights,
buff to the max, pull out your
contaminated bullet 12.7 Terminator, pop Vitality Powder + PTC (with PTA) for
90 AP, enough for two bursts per turn for 3 turns
(if you premeditate Stasis to keep your buffs live for one more turn). This should melt through anything and everything, especially on the third turn when Mag Dump + Jumpstarter MKII with 4 stacks gives you 19 bullets per burst.
Don't underestimate stealth; put points into it. You're not that durable without drugs, neither is your initiative great. Swapping to stealth armor set + Cloaking Device can help a lot before entering certain areas.
10 STR/10 PER/7 INT/4 CON. Put a point into CON at 16 to take Conditioning.
It might be possible to do the same build without Conditioning, and put the CON points into PER for max PER, but it is not easy to replace that 10% DR. If you use something like Kozozel, you're losing the PER you gained anyway; specialization points into Heavy Metal DR is your best option; but the accuracy boost from +2 PER may not be worth the damage loss from -5 Spec Points, plus the other benefits of Conditioning and 5 CON.
Footnote: The Builder is a bit bugged; Full Auto and Concentrated Fire can be taken with Heavy Guns, but in the editor I cannot, so I put 60 points in guns which won't be needed in game (only 25 for High Technicalities, so you can put points into Guns earlygame to use ARs better)