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)
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?
-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?
-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.
-Autocannons do not meet the criteria of suckage
There are plenty of other weapon systems in Battletech that suck. Bombast lasers, for example, are terrible. But they are fluffed as the hobby-horse of a specific manufacturer that started marketing the things when their engineers threw up their hands because they couldn't turn the system into anything workable. Bombast lasers are rare, basically a fluff curiosity that's just common enough to be worth having rules for. Rocket launchers also suck, and are fairly common, but they are fluffed as cheap weapons that are fielded in numbers only by the most budget-conscious forces that can afford little better. The Hunchback IIC is a bad mech, but it is designed such that it will occasionally perform outrageous acts of over-the-top heroism and carnage. Given the culture that uses this design, it's pretty clear why it would stick around the TO&Es of the clans.
Autocannons are ubiquitous, their diverse and numerous users all having somehow failed to notice how bad they are.
So, in short, all autocannons underperform. In general, 10s and 20s are usable while 2s and 5s are garbage. LBXs are the exception, with 2s and 5s having a niche as AAA and long-range crit seekers. LBXs have carved out a unique niche as vehicle killing weapons, AAA (although the big ones are a bit short ranged for that) and crit seekers. Standard autocannons and ultras need more help, with small caliber standards and ultras needing the most help of all.
So with all that in mind, here are my optional autocannon rules. They're intended to be used all at once, but obviously you can pick and choose if you think that wiser. They're also intended to keep existing designs legal and require minimal changes to the rules sheets. Finally, they're intended to be as simple as possible so as not to slow down gameplay. Obviously, the use of these rules will distort the battle value of any unit that has an autocannon.
Two-mode Fuse for Standard RoundsAutocannon "standard" ammunition is actually a marvel of miniaturized fusing technology. Variable-delay fusing existed in the mid 20th century, but the manufacturing technology that could transform crude, hand-adjusted fuses into induction-timed, proximity fused, mass produced munitions that were ubiquitous down to the lowly class-2 autocannons took a little more time. Essentially, autocannons are a hybrid HEAT/light armor piercing warhead with an electronically programmed fuse that can attack targets in two different ways.
Autocannon shells contain a forward-facing proximity sensor that can trigger their shaped-charge anti-armor warheads a few fractions of a second before impact. This gives optimal standoff and implosion geometry to get the most performance possible out of the warhead. Autocannon shells also have a light armor piercing cap internally and an all-aspect delayed impact fuse. If required, the proximity sensor can be switched off and the shells programmed to explode a few fractions of a second
after they smash into something. This mode is devastating to static structures like buildings and the internal structure of mechs, although it does a poor job of penetrating military-grade armor.
The standard mode is with the proximity fuse on, and in this mode all "standard" autocannon munitions (for ACs, LBX, RACs, UACs, etc) behave as normal. In delayed-fuse mode, the autocannon will do double damage to all buildings and all internal structure except for reinforced-type internal structure. In delayed-fuse mode the autocannon will do half damage to armor of all types except for armor with a BAR of less than 10, exclusive. The player attacking with the autocannon must decide which shell fusing mode they are using when they make the attack (the electronic fuse is set in the autocannon, the shells aren't smart enough to determine what they're about to hit).
Specialty ammunition types do not have a delayed-fuse mode.
Increased Damage Against Battle ArmorClass-2 autocannons of all types do 4 damage against battle armor when firing standard ammunition, based on whatever rationale bearhunter ACs do bonus damage to BA. Battle armor resists big hits well, but not lots of little hits that above some threshold. Or something. Class-5 autocannons of all types do 7 damage against battle armor while protomech autocannon-4s do 6 against BA.
This increased damage does not apply when firing any sort of specialty ammunition.
Increased Ammunition Per TonneAll standard autocannons have 140 damage per tonne of ammunition, so that's 70 rounds for -2s, 70 rounds for -5s, et cetera. Hyper-velocity autocannons are 80 damage per tonne of ammunition, so 40 for -2s, 4 for -20s, et cetera. Caseless autocannons have 200 damage per tonne of ammo. Protomech autocannons go up to a whopping 160 damage per tonne because (mutters something about superior clan technology, composite case designs, piezometric ceilings and efficiency) it would just be too hard to increase those by anything that isn't an integer since they pay per kilogram.
This situates autocannons between LRMs and SRMs for ammunition efficiency, enough that they wouldn't obviously be failing to pull their weight in centuries of campaigns' op-evals.
Optionally you can bump up gauss rifle ammo per tonne if you think gauss rifles should be inherently more ammo efficient than autocannons. Also, optionally, you can have all ammunition bins perform as though they have CASE, all CASE bins perform as though they have CASE II, and have all CASE II bins, and CASE II also prevents pilot damage from ammo explosions. The current ammo explosion rules penalize ammo weapons pretty heavily, and don't make very much sense. Isolated ammunition storage was pretty much a solved problem in the 1970s with the M1 Abrams. Why would things get so much worse in the 31st Century?
Autocannon FailuresUltra autocannon jams, standard autocannons using rapid-fire mode rules, and ammunition-related mishaps in caseless and hyper velocity autocannons can be un-jammed per rotary autocannon rules. Does it make any sense to you that a military would field weapons that have a 1/36 chance of bricking themselves as bread and butter for centuries? It didn't make any sense to me either. Caseless and hyper velocity are likewise so dangerously unreliable that they would obviously never leave the test stands, much less see limited production. Also, I thought it made more sense to consolidate jamming/failure rules on the various flavors of autocannon rather than have several different, and more punitive ones. The game gets slightly more streamlined, and an underperforming weapon category gets some love, win/win.
Ultra Autocannon HyperburstIn the late 20th Century, Soviet small arms engineers began work on a radical type of infantry rifle that combined an internally recoiling barrel with an extremely fast cycling burst mechanism in order to fire bursts that did not have their dispersion affected by the rifle's recoil. This work culminated in the AN-94 Abakan rifle, which saw limited issue into the early 21st Century.
Ultra Autocannons are that, but way bigger. The Soviet AN-94 had a mixed reputation for mass-produce-ability and reliability, so it obviously took some time before engineers were confident enough to attempt to scale up their design. Many a prototype ultra autocannon tore itself to pieces on the test range before the design was ready for mass production.
When firing in two-shot mode and at a single target (i.e. not using the multiple targets rules from TO), the to-hit roll is also a margin-of-success roll. If the to-hit roll is greater than the target number by 2 for UAC-2s, 3 for UAC-5s, 4 for UAC-10 and 5 for UAC-20s, then skip the cluster hits roll, both shots strike the same location. Roll for location normally. If the to-hit roll is greater than the target number, but not by the margins listed above, the number of shots that hit and the locations where they hit are resolved normally.
Counter-Defilade Mode for LBXIf a unit is obscured by cover that is the same height as the unit being obscured (e.g. a battlemech is hiding behind cover 2 levels tall), and the unit obscured is immediately adjacent to the cover it is obscured from its attacker by, LBX cluster munitions may be used to attack it per LRM indirect fire rules if there is a spotter. If the unit is obscured from its attacker by cover that is taller than the unit being obscured, or if it is hiding around a corner, then it cannot be attacked with LBX cluster munitions. The proximity sensor fuse time gate is "smart" but it isn't brilliant. Attempting to use the fuse settings to get the munition to detonate just behind a target when attacking it from the front is similarly out of the question.
LBX cluster munitions are essentially miniaturized, sensor-fused cluster bombs shot out of a cannon. Again, they are nothing that an early 21st century commander would be unfamiliar with, but great strides in manufacturing technology allowed these advanced munitions to be mass-manufactured and distributed out of the barrels of cannons like so much candy out of a pinata. Each cluster carrier has a proximity sensor that can be time-gated to ignore cover for a certain distance, and then go active once past a certain distance.
New Ammo TypesThe standard autocannon's feed system is admirably omnivorous, being able to load, fire, and extract a number of non-standard ammunition types that the original designers could never have foreseen. LBX autocannons use a high-low pressure system that prevents damage to the sophisticated electronics in the submunitions of their cluster shells, and as a result their ammunition is completely incompatible with standard autocannons, and vice versa. Ultra autocannons use counter-rotating revolving cylinders that also reciprocate and fire binary ammunition that is
wildly incompatible with anything exotic. Ultra autocannons are fidgety enough with the ammunition carefully tailored for them, sticking anything strange in their feed systems is totally out of the question! There was initial optimism at NAIS that rotary autocannons would prove compatible with a wide array of specialty munitions, but qualification trials have long since dashed that hope. The specialty munitions simply were not made robust enough to survive the high speed of the feed systems in RACs. Hyper-velocity autocannons and caseless autocannons have proven too rare to be worth furnishing with compatible, specialty ammunition although such ammunition could easily be developed if there were any demand for it.
But bog-standard autocannons proved able to accommodate several new ammunition types, even after the initial introduction of novel types in the late 31st century.
GLATGM ammo: Taking a page from Soviet tank designs of the late 20th century, designers realized that firing a missile (specifically, a Gun Launched Anti-Tank Guided Missile) out of a gun might be useful. Furthermore, the missile could be broken up into two parts that would be snap-assembled in the loading tray of the autocannon before being chambered in the gun (this is exactly how Russian gun-launched missiles work). The designers also realized that only the AC-20 had a wide enough bore to accommodate a worthwhile missile.
GLATGM ammo is for standard AC-20s only. GLATGM ammo is exactly the same as a thunderbolt-10 in terms of range and shots per ton, but it develops the same 7 heat as a standard AC-20 shot. For campaign purposes, it should not be considered interchangeable with thunderbolt-10 ammunition; the missiles have been designed from the ground up to work in autocannon feed systems.
HESH ammo HESH (High Explosive Squash Head) consists of a relatively thin-walled, insensitive explosive that deforms and flattens against the target. Once it has spread out an achieved maximum contact area with the target, it detonates, creating a shock wave inside the target that can cause spall to rip off of the inside of the target's armor plate. This effect can cause "scabbing" off of the inside of a target even if the HESH round doesn't penetrate. HESH is also particularly devastating against walls.
HESH ammunition was largely abandoned in the early 21st century due to the proliferation of early composite armors. However, the development of ultra-brissant, high-density explosives in later centuries made the concept viable once again.
HESH ammunition is for all standard and light autocannons. HESH ammunition does 2 points less damage than normal, down to a minimum of 1. HESH ammunition does double damage to buildings (so, 2, 6, 16, 36). HESH ammunition has a +1 to-hit modifier. HESH does half damage (round down) to battle armor and infantry. If a HESH round hits an armored target, but does not remove all of the armor on hitting it, and the amount of armor remaining on the target is equal to or less than the amount of damage the HESH round inflicted, roll on the determining critical hits table with a -1 modifier. If there are more points of armor remaining than the HESH round inflicted damage, there is no effect. If the HESH round removes all the armor and damages the internal structure, critical hits are resolved normally.
...
Thoughts?