Battletech: Main Gun Combatmath

Welcome back to more Battletech. Inspired by Hammer of Math, I have decided to compare out the various weapons that are commonly used as primary weapons on mechs. These weapons all tend to be mid-long range guns, but have very little in common otherwise. They vary wildly in damage and form, and several of them have interesting special rules or variations. The cutoff date for this article was 3067, as I had to draw a line somewhere for the sake of my own sanity, and most of the Dark Ages weapons are just exaggerated versions of previous ones. The AC20 and all missile weapons will also not be here, because those have fundamentally different roles to these weapons in my mind. I am sure that I missed one of the many, many weapons in this game, and I am very sorry if I did. I tried to stick to the Advanced tech level, so no experimental weapons.

Main guns in Battletech are a bit of a can of worms, because several of them are just kind of terrible and are incredibly disappointing to have on a mech instead of a more exciting weapon. Every weapon has its defenders, and while I am going to back my opinion up with math, there are always other things to consider.

Lyran Commonwealth Thug. Credit: SRM


For the math in this article I calculated out the expected damage of a given weapon at a series of ranges, that being 1, 5, 10, 15, and 20 hexes. This doesn’t line up perfectly with the range brackets of every weapon, but it should provide a reasonable range of data points. Some weapons are better in the transitional zones between these values than others, and, for example, if a weapon had a short range of 9, it would be the same from 1 out to 9. To calculate the expected damage, we are assuming that the firer is a Skill 4 pilot in a mech who walked, and the target is in the open with a TMM of 2 due to movement, as this is a very common set of modifiers and gives us a nice, average 7 as our starting TMM at short range. We then take the damage the weapon deals and multiply it by the chance to hit, giving us our expected damage. If a weapon can not hit at a specific range it is counted as 0 expected damage. This gives a good number for comparisons, as it allows weapons with a hit bonus, such as Pulse Lasers, or a hit penalty, such as Heavy Lasers, to be accounted for in the math.

In addition, for Cluster Table weapons, I did my best to calculate out the average damage they would do. With the Ultra AC this came out to about 40% more expected damage than a non-Ultra one, and with RACs it came out to 4 projectiles hitting. Bear in mind that the Ultras and RACs can sometimes do significantly more or less damage than the average presented here.

After all of the math, Ill add up all of the damage values at each range bracket, and then divide by the BV of the weapon, and get a Damage per BV value that should hopefully represent the advantage that longer ranged weapons get. 0.083 Damage per BV is the average of the whole data set, so that is the number to beat.

Highlander. Credit: Rockfish
Highlander. Credit: Rockfish


I have decided to separate the table out into weapon families for going over, as the unsorted chart is a mess to look at and weapons can fairly easily be grouped. Ill mention other categories whenever it is relevant to make a point. In addition, some of these weapons have special rules or considerations, such as the Plasma Rifle’s heat damage or the Snub PPCs long short range, that make them a bit harder to reduce down to a raw damage calculation. Also, there is a breakpoint at 12 damage, any weapon that can deal 12 or more damage is capable of taking a Mech’s head clean off in 1 shot, meaning that there is a small chance each time you shoot that you one hit kill the target outright. Most weapons pay pretty dearly for that advantage, but it can be enough to boost a weapon up in power by a lot.

In addition, some weapons are explosive while others are not. In a world with CASE that isn’t a huge deal, but not every mech has Case. Generally, all ACs have explosive ammo, and all energy weapons do not explode. Gauss Rifles explode themselves but their ammo isn’t explosive. This is a huge advantage for energy weapons in general, and I have known players who write off Ballistic weapons entirely due to this.

Another interesting wrinkle is that Energy weapons can sink all their heat for “Free”, assuming it is the first one you have put on your mech and you have “Free” engine heat sinks left over. A PPC or Large Laser is a lot better as a weapon if you are not paying for all the heat sinks that they take to fire, so mechs that can bracket fire well or simply don’t carry enough weapons to use all of their engine heat sinks get fantastic use out of those weapons, which the BV ratio doesn’t reflect super well. They also are considerably better with Double Heat Sinks, with some weapons, such as the Heavy Large Laser, being total insanity to imagine using without them. Clan DHS are better, but even Inner Sphere ones are a huge upgrade and go a long way towards evening things out across the board.

If you are using Single Heat Sinks, or you have already used all of your “Free” engine double heat sinks, an Autocannon or Gauss Rifle becomes more tempting, as they don’t generate a lot of heat, and can even be added without any heat sinks, if you are willing to build a few heat a turn and ride your heat index. If we assume CASE and Double Heat Sinks exist and are being used, the balance between Ballistic weapons and Energy weapons is fairly good, with a few exceptions.


Weapon1 Hex5 Hexes10 Hexes15 Hexes20 HexesBVDamage Per BV
LBX AC20.161.160.560.560.16420.062
Clan LBX AC20.
Ultra AC20.481.650.80.80.23560.071
Clan Ultra AC20.81.650.80.80.23620.069
Rotary AC24.644.642.240.6401180.103
Light AC21.161.160.560.160300.101

Starting out with the smallest and most piddly of the weapon types, AC2s are in my opinion mostly bad. The damage per BV is fairly low, with the Rotary AC2 and Light AC2 both being better than average. This is mostly due to the huge damage of the RAC, and the low BV and lack of minimum range on the Light AC2. These weapons do have a niche in having pretty extreme range on average, and are pretty good at shooting down Aircraft if you are playing with Aerospace rules. There are better options for both of those roles though. 2 Damage is a massive hill to climb and for the most part these weapons don’t do it. An interesting note for all the AC families is that the LBX autocannons can fire cluster shot, which is very good if you are trying to crit your opponent in a specific location as they generate more hit location rolls than any other weapon. Cluster Shot also has a to-hit bonus, which makes that crit seeking even easier.


Weapon1 Hex5 Hexes10 Hexes15 Hexes20 HexesBVDamage Per BV
LBX AC 50.852.
Clan LBX AC50.852.
Ultra AC51.994.121.990.570.571120.083
Clan Ultra AC51.994.121.990.570.571220.076
Rotary AC511.611.65.61.602470.123
Light AC52.

The genesis of this article is an argument I had years ago with someone over whether the AC5 was a good weapon or not. I have never been a fan of it, because it feels like such a small amount of damage for such a heavy, large weapon. According to the math, it definitely shakes out to be worse than average, though not by as much as I personally feel it is. The RAC5 and Light AC5 continue the trend from the AC2 versions of being way, way better than the other AC5s, being tied for third best weapon in the whole set, with the RAC being capable of some truly horrific damage spikes from time to time.

The Ultra AC5 is amusingly exactly an average weapon, which checks out. AC5s do have slightly longer ranges than their closest competitors, but in my mind that is not a big enough advantage to make up for the small hit and mediocre Damage to BV ratio. Another big problem with AC5s is that they are really heavy for a weapon that does 5 damage, weighing 8 tons, 9 with ammo. This means that a mech really can’t have that many of them, and you spend a lot of BV on the chassis of the mech, its Armor, and its Engine, and putting an AC5 on it feels like a waste of the BV of the “Naked” mech compared to something like a Large Laser.


Weapon1 Hex5 Hexes10 Hexes15 Hexes20 HexesBVDamage Per BV
CERPPC (Praise Be)
Heavy PPC2.558.74.21.203170.053
Light PPC0.852.91.40.40880.063
Snub Nosed PPC5.
Plasma Rifle5.

This Dataset was an absolute flashbang to my soul. I have always been of the opinion that PPCs were some of the best weapons in the game from a pure damage standpoint, and that is blatantly untrue according to the data. The fact that the AC5 has a better damage to BV than any of the PPCs save the Snub Nose feels so wrong on such a fundamental level. PPCs are also incredibly heat intensive and thirsty for heat sinks, which can rapidly drive their weight up towards insanity depending on heat sink tech and whether you have engine heat sinking capacity left over from your other equipment. If you have engine heat sinks left over, the PPC will be better compared to if you have to put each and every heat sink on the mech to support it.

That all being said, PPCs do have several good traits over the AC5 that go a long way towards pulling them back towards better. For one, the Clan ER PPC and Heavy PPC are both Head Choppers and have a chance at instantly killing anything they shoot at, with the Clan PPC being one of the conventional “Best” weapons in the game, even with its huge BV cost. PPCs overall do a single 10 to 15 damage hit, which is powerful, as it can open up hit locations for crits a lot better than two 5 damage hits. Single powerful hits are generally more powerful than multiple small hits in Battletech, unless you are trying to crit a location that has already been opened up. These weapons also don’t run into the issue of lost BV from the mech’s chassis, as anything with a PPC can be expected to perform pretty well compared to an AC5. Personally I am a Marik at heart and prefer the Large Laser family of weapons to these, but the long ranges and large hits are very strong.

The Snub PPC needs a specific call out, as it has an incredibly long short range of 9 hexes, but falls off hard at longer ranges, having small medium and large range brackets, as well as literally doing less damage at longer ranges. If it is on a fast mech that can stay up close, it can be one of the most efficient weapons on the list.

The Plasma Rifle is another weirdo weapon that got stuck in the PPC category mostly because of damage, as it is an energy weapon that requires ammo. Its ammo is not explosive though. It also can inflict heat on enemy mechs, which, if combod with Inferno SRMs, can let you overheat enemy mechs and make them easy pickings, which is incredibly interesting and can be very fun.

Large Lasers

Weapon1 Hex5 Hexes10 Hexes15 Hexes20 HexesBVDamage Per BV
Large Laser4.644.642.240.6401230.099
ER Large Laser4.644.642.240.6401630.075
Clan ER LL5.
Heavy Large Laser6.726.722.720.4802440.068
Large Pulse Laser7.475.222.52001190.128
Clan LPL (Praise Be)

Large Lasers are my favorite category of weapon personally, and from a BV perspective that is a justified opinion. They do have the same issue as PPCs where their weight can get out of control after you have used all your engine heat sinks, but to a lesser extent for the most part. I love the basic Large Laser to pieces, and it is, indeed, better than an AC5 from an expected damage standpoint everywhere but 16-18 hexes, where the Large Laser gets outranged. In my mind this is a reasonable trade for significantly better damage, no minimum range, and a better ratio.

The Large Pulse Laser is, according to the math, the best weapon in the data set in terms of BV to Damage dealt, as its hit bonus allows it to boost it’s expected damage up by a lot compared to other weapons. The Clan version is, in my mind, better even though it has a worse ratio, as the range on the basic LPL is pretty pathetic by comparison. The Clan LPL has a pretty good damage to BV ratio, and a pretty good range, outranging most other weapons and delivering a nasty 10 damage hit with a gigantic hit bonus. In my opinion it is the overall “Best” weapon in the game, though arguments can be made for a variety of other weapons.

The Heavy Large Laser here is an interesting case, as it is a head chopper, but it has a to hit penalty, so you deliver hits less often than with other weapons. In addition, the heat that comes out of a Heavy Large Laser is some of the most extreme in the entire game, a humongous 18 points, which makes its weight spiral into the stratosphere once you account for heat sinks. The ER Large Laser is a somewhat bad upgrade to the basic Large Laser, as the basic Large Laser is one of the more efficient weapons in the game, getting basically nothing but 4 hexes of extra range at the cost of 50% more heat and a good chunk of extra BV. It is longer range, but in my mind that trade is not worth it. The Clan Variant does more damage and has 10 hexes of extra range, making it one of the premier sniping weapons in the game. You do pay for it though, with it having a pretty bad damage to BV ratio, but the extra range here matters in a pretty huge way, and it is still better than most of the PPCs from a BV standpoint while doing nearly the same amount of damage.


Weapon1 Hex5 Hexes10 Hexes15 Hexes20 HexesBVDamage Per BV
Gauss Rifle4.
Clan Gauss Rifle4.
Light Gauss Rifle1.364.642.242.240.641590.070
Heavy Gauss214.

Gauss Weapons are the most efficient headchoppers in the game, and are generally great weapons. They have good range and horrifying damage across the board. They are quite heavy no matter what, and unlike energy weapons, they don’t get any lighter from having Double Heat Sinks. The Light Gauss is not a headchopper, which is a bummer, and overall is by far the worst Gauss weapon, only really having a niche on some IS light mechs, as it does 7 less damage than a Gauss rifle and weighs the same as a Clan Gauss Rifle.

The Heavy Gauss Rifle has the same damage falloff as the Snub Nosed PPC, and has a minimum range which massively hurts it, but it puts the hurt on things like no other weapon in the game can if used perfectly. I generally favor more consistent weapons and would rate the normal Gauss weapons a lot higher, but there is an argument to be made here. According to the math, if you want to one shot mechs from extreme ranges, these are the best weapons to do that with.


Weapon1 Hex5 Hexes10 Hexes15 Hexes20 HexesBVDamage Per BV
LBX AC105.
Clan LBX AC105.
Ultra AC108.
Clan Ultra AC108.

Oh God oh no House Davion was right the whole time, the AC 10 really is the ultimate weapon. This one shocked me a bit aswell, as I was completely unprepared for AC10s to be, on average, the best weapon category in the game. The basic AC10 is the second best weapon in this dataset at converting BV into Damage, and all the other variants trade a worse (But still much better than average) ratio for good secondary/special effects. The Ultra AC10 has the chance to just rip it and do 20 damage, and the LBXs are excellent at killing infantry, helicopters, and planes with their cluster shot. LBX and Ultra AC10s also have the same range as an AC5 or PPC, putting them in that longer range belt, which is an advantage. The Base AC/10 is also probably the best weapon to give the Special Autocannon Ammo to, which is really fun and you should use it.

Clan Wolf Beta Galaxy Ryoken III. Credit: Jack Hunter


Overall the general takeaway from this article is that Small Bore Autocannons suck in their base state, with only the Light versions and Rotary versions being good, and they could use a BV reduction at some point if Catalyst is interested in adjusting the BV algorithm. The AC5 is almost a median weapon from a Damage to BV standpoint, and it has good range, but the small hit and opportunity cost of spending 10 tons and a mech chassis to do 5 damage in my opinion holds it back from being decent. Other takeaways are that PPCs have a kind of bad BV to Damage ratio, and are heavy and heat-intensive compared to the AC-10, which is apparently a godly weapon we should all kneel before and pray for salvation.

I was shocked by the PPCs not doing well here, as they had kind of been in the back of my head for the last decade as the “Best” weapons in the game. Large Lasers are very solid and reliable, with basically nothing in that category being super disappointing, my distaste for the IS ER Large Laser aside. If you want to Head Chop someone, you are best off going for a Gauss Rifle rather than a Clan ER PPC, as they cost less BV for similar damage. The ER PPC might be better if it is your first weapon and you can sink it completely with your engine heat sinks as it will be much lighter than a Gauss, and does have the advantage of not blowing up and having unlimited ammo.

My personal picks for the “Best” weapon in the game after looking at all of this would be either of the Large Pulse Lasers, and the AC10s. None of them can head chop, but the AC10 is very cheap and efficient, and the Large Pulse Lasers are super consistent due to their hit bonus cutting through negative hit modifiers from terrain and movement. I personally don’t like counting on Headchopping as a tactic, as in my opinion it doesn’t happen often enough to be worth sacrificing more efficient and reliable damage for, but you can spam enough headchopping weapons to make it work.

None of this math really matters though, because I’ll still get shot in the Center Torso by a “Weak” and “Pathetic” AC2 on the first turn and get TAC’d to the Gyro, but we can at least try to get some optimization out of this horribly unoptimized game.