So I don't derail the Great Wyrm MOTW article with a rant about how unconscionably bad autocannons are in battletech, I thought I would put forward some homebrew rules to make these things viable. Maybe not amazing, and certainly no match for the cheesy glory that is clan energy weaponry, but at least good enough that I am comfortable with them.
The reason I'm currently uncomfortable with autocannons is because they break my suspension of disbelief. Under the current rules, autocannons are basically so bad that either their representation vs. other weapons is drastically uncharitable, or all the clans, great houses and minor powers have had a centuries-long lapse of sanity in continuing to field these things.
Here are my beefs with autocannons:
-Autocannons have poor damage per tonne of ammunition compared to missiles. Once you account for missile scattering, autocannons pull slightly ahead of LRMs, but they are still squarely behind SRMs. Streak SRMs, of course, clobber autocannons in terms of efficiency (and everything else that isn't an energy weapon)
OK, let's start right there. I'm assuming you're looking at max damage...which almost never happens in-game. But since it also mirrors what happens when the ammo explodes, we can take a look at it:
- MRMs: 240 points per ton
- LRMs: 120 points per ton
- SRMs: 200 points (SRM-2/-4) or 180 points (SRM-6) per ton
- ACs: 100 points (Class 5/10/20) or 90 points (Class 2) per ton
If you mean "poor" because of the damage you take from an ammo explosion...believe me, you'll prefer "poor" any day. But even with that, they're pretty much on par with LRMs.
Now, since you addressed missile scatter, we'll go ahead & deal with that. First, I'm assuming we're dealing with standard autocannons (or possibly the later Light ACs), & avoiding the specialty Ultras, Rotaries, & LB-X variants; otherwise, we'd have to consider the Artemis IV, Narc-following, & other specialty missiles. Missile scatter actually brings up an important note. Missile launchers scatter their hits: LRM/MRM volleys are resolved in 5-point damage groups, & SRMs all hit different locations. Even Streaks hit different locations, they're just a binary solution launcher (either the launcher locks on & all missiles hit the target, or the launcher doesn't lock on & 0 missiles hit the target). That means at best, an SRM launcher's attacks are the equivalent of an AC/2 shot, & an LRM/MRM damage group is equivalent to an AC/5 shot. All the larger launchers do is give you more of those smaller hits, giving you a shotgun-style effect on the target. ACs, however, just do single hits to their target; maybe not so impressive for the Class 2 or 5 versions, but an AC/10 will worry a Light 'Mech, & an AC/20 makes even a Heavy or Assault 'Mech think twice about getting in close.
This doesn't make any sense, either from a real-world engineering perspective or from a game balance perspective. Compare the M456 105mm HEAT round from the mighty L7 tank cannon to an RPG-29, which is also 105mm. The 105mm gun round is much faster, but also much smaller than the RPG-29. On the other hand, high-velocity 105mm tank guns are way too heavy for infantry to carry around, but missile launchers are not. So rocket propelled munitions are a trade-off; the ammunition is much bigger and heavier, but the launchers themselves are much lighter. The reasons for this are fundamental to internal ballistics, and so unlikely to change in the future. Battletech gets this halfway right, of course; the guns are heavier than the rocket launchers... but the ammo is effectively heavier too (less damage/tonne). Why would anyone use these awful things?
Probably because the Autocannons are actually superior to the real-world guns you described? Remember, BattleTech armor is
not equivalent to the real-world armor used on tanks -- which, even on high-tech models like the Abrams, can still have an anti-tank round penetrate the armor before the entire armor on that section is vaporized. That's more like the BAR armor used on Support Vehicles (which in-universe were "the" combat vehicles before Combat Vehicles were officially introduced, as shown by the "primitive" models in the various
Technical Readouts). Unless you manage to put BAR 10 armor on the Support Vehicle (an impossibility for Tech Level A units, equivalent to 19th- or early 20th-century vehicles; Tech Level B units can use it, but they need the Armored Chassis modification, & they only get 4 points per ton of armor, 1/4th the protection that BattleMech standard armor provides), you have to worry about penetrating hits even if your armor isn't depleted. Heck, you could have a max-armor 100-ton TL B Tracked vehicle (204 total points of armor, with easily 50 points on the Front, 40 points per Side, 30 points Rear, & 44 points Turret), but with BAR 6 armor a Heavy Rifle (9 points) has a chance on every hit of punching through & inflicting a critical hit, let alone a Large Laser, AC/10, PPC, or Gauss Rifle. That's more like real-world tank battles, where tanks are "killed" (or at least "mission-killed") because they take penetrating hits to critical systems, & unless that critical system is a fuel tank or ammo bin they're crippled-but-still-mostly-intact blocks of metal on the battlefield.
BattleMechs, OTOH, are different. Aside from the very low chances for random critical hits (either by that 1-in-36 chance of rolling 2 on the Hit Location Table, or by using specialized ammo), critical hits can't happen until the armor in a section is completely gone. Imagine if you could upgrade an Abrams with armor that functioned like that, & how truly difficult to take out it would be.
-Autocannons have poor damage output relative to tonnage.
This doesn't make sense from an in-universe perspective. Most battles in the BT universe are fought at the end of lightyears-long logistical trains, and attacking forces are constrained by what they can cram into their dropships. Surely generals and engineers would try to economize on tonnage, and try to use only weapons that give the most zap for the least weight? Surely, after centuries of warfare spread over nearly all the worlds that man has ever colonized, someone would have realized that autocannons completely suck and they should be using almost anything else instead?
This depends on how you look at it. First off, I think it's deceptive if we simply look at the weapon stats as-is, vs. the additional "support" equipment they require. Yes, autocannons & missiles won't function if they don't have ammo, so we have to account for their ammo tonnage when we look at any kind of comparisons involving tonnage. By the same token, however,
all weapons, (especially) including energy weapons, need heat sinks to offset their heat. Yes, yes, I know: every BattleMech comes with 10 "free" heat sinks. But very few 'Mech designs, especially those with a lot of weapon systems, &
especially those with a lot of energy weapons (I'm looking at you, Clan 'Mechs), have only 10 heat sinks (single or double) in them. And once your weapon heat exceeds 10, you're pretty much adding heat sinks every time you add another weapon system. Now, I'm going to ignore the situation of Combat Vehicles -- aside from the fact that they don't need heat sinks for ACs & missiles, they also have that situation where ICE-powered units not only have to spend tonnage on their heat sinks for energy weapons, but they need power amplifiers for them as well. So for this situation, we're going to look at it in the abstract, & go with the following requirements:
-- for now, we'll ignore advanced technology like Ultra ACs, Pulse Lasers, ER Lasers/PPCs, LB-X cannons, Gauss Rifles, etc., sticking with Introductory tech. We'll also ignore Machine Guns; they don't generate heat, & they have massive amounts of ammo per ton, so their results end up pretty skewed.
-- For ammunition requirements, all weapons must have at least 10 shots each. Aside from the AC/20 (2 tons), LRM-15 (2 tons), & LRM-20 (2 tons), all of the other weapons only need 1 ton of ammo.
-- For heat purposes, every heat point generated by a weapon has to be offset by a heat sink. Yes, this means that a PPC has to add in 10 heat sinks for its 10 heat points, while an AC/5 only adds 1 heat sink. Note that, since we're not considering advanced weapons, we're also not considering double heat sinks.
-- In addition to calculating the damage per ton, I'm also calculating the tons per critical slot. This is because there's more than one way to measure efficiency. Wanting to pack the most damage into your 'Mech is good, but sometimes you can find yourself running out of space in your 'Mech before you've run out of tonnage. That's because some weapons are actually quite bulky (i.e. their tonnage-to-slot ratio is low), compared to other weapons.
-- For the ballistic & energy weapons, we're using maximum damage. For missiles, the first number is the average number (i.e. assuming a 7 is rolled for Cluster Hits), while the number in parenthesis assumes maximum damage; since that rarely happens (aside from the SRM-2, which needs an 8+, all the other stock missile launchers need an 11+ on the table to get max damage).
With those adjustments, this is what we end up with:
-- AC/2: 8 tons, 3 critical slots; 0.250 damage/ton; 2.333 tons/critical slot
-- AC/5: 10 tons, 6 critical slots; 0.500 damage/ton; 1.667 tons/critical slot
-- AC/10: 16 tons, 11 critical slots; 0.625 damage/ton; 1.455 tons/critical slot
-- AC/20: 23 tons, 13 critical slots; 0.870 damage/ton; 1.769 tons/critical slot
-- PPC: 17 tons, 13 critical slots; 0.588 damage/ton; 1.308 tons/critical slot
-- LL: 13 tons, 10 critical slots; 0.615 damage/ton; 1.300 tons/critical slot
-- ML: 5 tons, 4 critical slots; 1.000 damage/ton; 1.250 tons/critical slot
-- SL: 1.5 tons, 3 critical slots; 2.000 damage/ton; 0.500 tons/critical slot
-- LRM-5: 5 tons, 4 critical slots; 0.600 (1.000) damage/ton; 1.250 tons/critical slot
-- LRM-10: 10 tons, 7 critical slots; 0.600 (1.000) damage/ton; 1.429 tons/critical slot
-- LRM-15: 14 tons, 10 critical slots; 0.643 (1.071) damage/ton; 1.400 tons/critical slot
-- LRM-20: 18 tons, 13 critical slots; 0.667 (1.111) damage/ton; 1.385 tons/critical slot
-- SRM-2: 4 tons, 4 critical slots; 0.500 (1.000) damage/ton; 1.000 tons/critical slot
-- SRM-4: 6 tons, 5 critical slots; 0.667 (1.333) damage/ton; 1.200 tons/critical slot
-- SRM-6: 8 tons, 7 critical slots; 1.000 (1.500) damage/ton; 1.143 tons/critical slot
We can then rank them on their efficiency with these numbers. Although I provided the maximum damage figures for the missile launchers, I'll omit them for now because they seldom do their maximum damage (1 out of 12 times, on average).
Most efficient by damage/ton (average damage):
- Small Laser
- SRM-6
- Medium Laser (tie)
- AC/20
- LRM-20, SRM-4 (tie)
Least efficient by damage/ton (average damage):
- AC/2
- AC/5
- SRM-2 (tie)
- PPC
- LRM-5, LRM-10 (tie)
So, we had a couple of energy weapons in the Top 5, but we also had an Autocannon, the mighty AC/20. And while the AC/2 & AC/5 topped the Bottom 5, we also saw the "mighty" PPC on that list (4th-worst). And both the top & bottom had missile launchers in them. More importantly, there was a much bigger gap in performance between #1 & #2 on the Top 5 list than there was between #1 & #5 on the Bottom 5 List. In other words, if you're looking for the most bang for the tonnage in your design, you have options from all 3 categories (including options you may want to avoid).
On the other hand, efficient use of space spotlights where autocannons excel. If you have a 'Mech that doesn't have a lot of tonnage available (i.e. a fast Light or Medium 'Mech), you probably will focus on energy weapons & missile launchers, because the weapons are individually light, & you may have such limited tonnage that you can get by with those 10 "free" heat sinks (i.e. like the STG-3R
Stinger, which needs no extra heat sinks to jump & fire its Medium Laser & MG...at least until it takes an AC/10 or PPC hit to a leg, or especially a Large Laser to the head...). But if you have a Heavy or Assault 'Mech, it's a lot harder to build a Medium Laser "Boat", or even a Large Laser "Boat", without starting to worry about space. On the other hand, slap in an autocannon, & you have the space left to pad it with some Medium or Small Lasers as backups.
-Autocannons are significantly less flexible than missiles.
This is a pure game balance perspective. A rocket motor offers much more gradual acceleration than the barrel of a gun, so it makes sense that more sophisticated and delicate electronics could be stuffed into the nose of a missile than into the shell of an autocannon. But if a weapon is basically bad, but still commonly fielded by almost everyone, I would reasonably expect it to do something cool on the side to balance out its lack of obvious merit.
Can't say I necessarily agree here...unless you mean by "flexible" their ability to scatter & simultaneously spread their damage all over a 'Mech, instead of dealing the damage to a single spot. With an energy or ballistic weapon (barring cluster rounds), each shot does 100% of its damage to a single location. That's why the AC/20 (& advanced-tech items like the Gauss & Heavy Gauss Rifles, or the Clan's ER PPC & Heavy Laser) have a built-in boost on their BV: if you can roll boxcars on your Hit Location roll, a single shot will wipe out the Head of the 'Mech.
And sometimes it's nice to be able to have the extra oomph behind a single devastating blow. I know the
Hunchback IIC was mentioned in passing
[snip]
Sorry, it's cutting off my response, so I'll have to post it in parts.