Why You Should Actually Trust BattleTech’s Mysteriously Short-Ranged Autocannons

Courtesy of EldoniousRex

So it’s been a few years since I wrote an article that compared BattleTech’s autocannon rounds to high explosive pancakes, and while it was a fun piece to write, something has always bothered me about it. There were a lot of responses, all of them from folks much more knowledgeable than myself about military ballistics I’m sure, and they all seemed to make valid points on why a gun’s bore size doesn’t necessarily mean anything when it comes to effective range.

Notably, none of the comments really went over my math to disprove that BattleTech’s cannon munitions are not actually flat discs, so I’m pretty confident that I can convince CGL to one day accept my article as irrefutable truth.

But the range thing--that’s stuck with me. Of course, writing for Sarna is a busy job what with all the BattleTech news that never seems to end (go read Sarna’s recent March news blast to find out what’s going on with MechWarrior 5 and MechWarrior Online, by the way), so I never got the chance to actually go through all those comments to see just what the heck they were talking about.

Until now. Yes, four years later, I’m taking a dive into the deep end of artillery to see just how a larger gun can shoot a bigger bullet not as far as a smaller gun firing a tinier shell.

And my journey starts with, of all people, Tex of the Black Pants Legion.

From my previous interview and listening to the Black Pants Legion podcast, I knew that Tex was a gun nut and also a military historian, so I figured if anybody knew a thing or two about guns, it’d be him. Sadly, Tex is a busy guy and I wasn’t able to get a full interview, but he was able to point me in the right direction while desperately defending his homestead from COVID zombies.

“Sean, you fuckwit,” I can clearly recall him telling me over a brief Discord call. “Barrel size doesn’t mean jack shit. There’s way more that goes into making a shell go zoom, like stabilization, recoil reduction, heat dissipation, and propellant. Look, you’re a smart guy, just check out this Italian naval cannon and you’ll figure it out.”

Then he hung up after several loud gunshots. I assume he’s fine.

That Italian naval cannon, by the by, was the Oto Melara 76mm autocannon, perhaps one of the best examples you can find today of what an autocannon from the year 3025 might look like. And as I researched the Oto Melara, I was surprised to find that it possessed qualities that seemed to belie its diminutive bore size.

76mm SR
Watch this video on YouTube.

For those unaware, bore size refers to the diameter of the barrel and is often used as a rough measurement to describe a gun’s overall size. However, it is but one measurement of many, and it can often obscure a cannon’s true power.

If you’ll remember from my previous article, the general rule with guns is that the bigger they are the farther they’ll shoot; an M1911 semi-automatic pistol will never be able to shoot as far as an M119 howitzer no matter how much you rearrange the numbers one and nine. But once you get into the artillery range of cannon sizes, things get a lot more… complicated.

The problem with ballistics is that there are way too many factors that’ll determine a gun’s maximum range. That said, we can narrow things down to a few topics and then discuss how those factors could contribute to BattleTech‘s inverse relationship when it comes to bigger guns firing over shorter distances.

The Bigger The Boom, The Bigger The Boomstick

The factors leading to a projectile traveling as far as it can are numerous, but they always start with the same thing: a really big explosion. That explosion then needs to be contained and directed down a barrel that won’t also explode along with the shell that the explosion is pushing. Then there needs to be recoil dampening, exhaust evacuation, and a loading mechanism, all of which need to be appropriately balanced in order to maximize performance.

And that’s what I think Tex was alluding to when he pointed me at that Italian naval cannon. In order for BattleTech’s autocannons to be mounted on a ‘Mech at all, they need to sacrifice some of the factors that allow a cannon to fire with longer range.

Let’s take the Oto Melara 76 mm as a starting point and compare it to the M119 105 mm howitzer. The Oto Melara has a maximum firing range of 20 km, while the howitzer has a maximum range of 17.5 km. The Howitzer fires a larger shell (105 mm), but the smaller shell of the Oto Melara not only flies further, but it also has a lot of friends with a fire rate of about 80 rounds per minute. The M119, on the other hand, struggles to fire 3 rounds per minute with a well-trained crew.

One is a manned field artillery piece designed to be carried on the back of a truck. The other is installed in a naval turret with an automated loader mechanism and radar-assisted fire control. There’s a lot more going on with the Oto Melara to allow its shells to exceed that of the field howitzer, but the point is that a big shell doesn’t always mean one that’ll go far when the cannon goes boom.

Are you my daddy?

We can see an even better example of this by heading back to the final days of World War 2. The Sturmtiger has a gaping 380 mm barrel that’s barely a few feet long--sort of like how you see on certain ‘Mechs such as the Cauldron Born-B, Thunder, and Emperor. Because the German designers tried to shoehorn an enormous gun onto what was essentially a mobile bunker, enormous sacrifices were made to range and fire rate, such that the rounds fired from the Sturmtiger were more like mortar shots with a range of roughly 5 km.

Compare that to something like the 16-inch (406 mm) naval guns on most US battleships of the same era, which had a range of over 40 km, and you see just how meaningless a gun’s bore size can be.

You Need Space To Shine

So what does a cannon need to lob a round as far as it can? Well, as the guns of the Mighty Mo prove, you need a big-ass barrel, a ton of propellant, and something for that propellant to explode against that won’t shatter into a million pieces (and also probably sink the ship that’s firing the round).

Let’s maintain our comparison between the 16-inch guns of the USS Missouri and the Sturmtiger to further prove this point. To get that 43km range, Mighty Mo used six propellant bags that weighed roughly 100 lbs each. The barrel was about 67 feet long, and the whole gun including the breach weighed roughly 134 tons.

Now the Sturmtiger. To ensure that it didn’t blow up every time it fired, the Sturmtiger’s rounds were technically rockets that were integrated into the 830 lb projectile. The barrel was only about 8-feet long, which wasn’t even that much more than the 5-foot long shell itself. And in order to be mobile at all, the gun itself had to be relatively light in order to fit onto the Sturmtiger’s chassis, which topped out at 75 tons.

The Sturmtiger is just like an AC/20 in BattleTech. It had to sacrifice so much in terms of barrel length and gun mass just to fit onto a mobile chassis like a ‘Mech that it lost all the important bits that let a cannon fire like it was Iwo Jima in 1945.

Expand this concept to the rest of BattleTech‘s autocannon line and it doesn’t sound all that unbelievable that the smaller a gun gets the longer its range. To help drive this concept home, I’ve made a series of charts that compare historical weapons and autocannons. Note that the axes are not to any particular scale.

Here we have historical cannons. Note the trend that as a cannon gets larger its attendant vehicle needs to also get larger to maintain that gun’s performance.

Now check out the same chart I made for ‘Mechs and autocannons. Note that ‘Mechs don’t vary nearly as widely as historical military vehicles, so bigger autocannons sacrifice range to stay viable on the platform.

And there you have it. Big guns need big vehicles, and if you don’t get bigger, then those guns have to lose explosive power resulting in less range. BattleTech’s autocannons are not stupid at all and are in fact a clever recreation of what would actually happen if you tried to stick giant cannons onto a giant robot.

Of course, this completely ignores the fact that not all autocannons have the same caliber, even amongst the same class. An AC/20 could be a rapid-firing 120mm cannon or a giant mortar-style 300mm cannon (or anywhere in between) with damage values merely representing their destructive capacity and nothing else.

But that’s a topic for another time.

And as always MechWarriors: Stay Syrupy.

stay syrupy

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About Sean

Hooked on BattleTech at an early age, Sean honestly can't remember whether it was the cartoon, the serial novels or the short-lived TCG that did him in. Whatever it was, his passion for giant shooty robots never died, so now he writes about the latest and greatest in 'Mech related news.

17 thoughts on “Why You Should Actually Trust BattleTech’s Mysteriously Short-Ranged Autocannons

  1. Flashfreeze

    As an avid player of World of Tanks, I have often joked with my fellow platoon-mates (themselves Battletech/Mechwarrior fans) that the 152mm howitzers on the infamous Russian KV-2 and SU/ISU-152 vehicles were actually AC/20s in disguise.

    Considering the damage done in a single hit from one of those, no one’s yet disagreed with me…

    Reply
    1. Suralin

      Since I was farting around with WW2 tech in my “Why oh why did I stat out the Panzer I” thread, I have the Soviet 152 fluffed as being AC/10 levels of damage, but only against BAR 5 and below (so usually good enough to one-shot a target anyway). Against higher-tech stuff, it’s only as effective as a Mech Mortar/4. But that’s still really good for an ancient gun like that, IMO.

      Reply
  2. BlackCatActual

    The Sturmtiger still shoot up to 5km, that’s 5000 meters. Ac20s go, what? 300 m at best before their damage values fall off.

    Reply
    1. David

      The Sturmtiger is a wheeled platform at least weighing 75 tons, and the actual gun and gun-support requirements are over half the mass of the tank.

      A Battlemech is a bipedal walking platform with a lot more gear that somehow fits onto a 50 ton (Hunchback) chassis, with most or all of the weapons located well above the center of mass balance point, especially since we almost always see AC/20s located as a shoulder mount.

      Consider the engineering compromises that would need to be made and how they would affect range:
      – chopping that Sturmtiger’s gun down to a mere 14 tons weight (the canonical weight of the Hunchback’s AC/20).
      – loading it well above the center of mass instead of pretty near the center of mass like on a tank.
      – Stabilizing it enough, again considering a bipedal chassis rather than the usual tripedal or quadrangle footprint of a mobile howitzer or a tank, so that it doesn’t COMPLETELY throw off the firing solutions for the other weapons on the ‘mech every time it is fired.

      Also remember, this isn’t a question of “theoretically where could a missed shot end up” but instead “range in which the pilot could point at a moving target and have some reasonable, better-than-a-snowball’s-chance-in-hell chance of hitting what they aimed for.”

      It’s the same way that hunters are advised to always know what they are aiming for, because a shot from a hunting rifle can TRAVEL a couple of miles (upwards of 7000 yards) but “effective, reasonable probability you hit what you aimed for” range is FAR LESS. Most whitetails and mule deer are killed at distances of 200 yards or less, with “extreme long range” shot attempts (if your target is standing still and you have plenty of time to line up your shot) out in the 300-400 yard range.

      Reply
  3. Garrison Chisholm

    I’ve always pondered the following example;

    Your target, a crafty low-life Locust on 1 leg, is 300m away, and you are in a Hunchback. Your AC20 would pulverize him, but- what happens to your shell at 271m that didn’t happen at 270? Shouldn’t there be some rule about the momentum that seemingly evaporates magically from your round? Now consider a GM running a serious long-term MW game, and place your foul Locust in front of a Children’s hospital 100m high and 200m broad.
    (Ok yeah i know, but just go with it) – isn’t the GM now *compelled* to rule on what happens to that shell in meters 271-300, that 10th hex holding the hospital?

    If you are desperate to shoehorn physics into your gaming, say that at 271m the shell “loses the required excess velocity to qualify as a noteworthy volatile against 31st Century targets”, but in truth, the game happens. If it matters to the GM’s story what happens to the shell, they legislate what happens. If you’re just playing the boardgame, it doesn’t matter at all. Fiat.

    Reply
    1. Poxinabox

      Ooh! I can be helpful!

      This actually is covered in Tac Ops on page 85, Garrison. We implemented it in my campaign and after doing the calculations the first time it just gets easier to use. Mind you, it’s incredibly hard for my players to hit the faster targets at their skill rate, but the slower ones take a good glancing shot of a portion of the stated damage.

      Basically anything beyond long range is in extreme range, and depending on the weapon it scatters, does reduced damage, or both.

      Reply
  4. MookieDog

    Not a bat article. Understood this issue has been discussed a lot. Having been a Bradly ODS Commander for almost eighteen months and having been playing BattleTech since 87, I have seen both sides pummel each other to death. After hearing both sides ad nauseum, the simple fact is: you can not compare the universe of big stompy robot weapons to what we have current day. You just cant.

    We have 120mm smooth bore APFDS rounds that can effectively engage and kill targets at 3K. 3000 meters in BattleTech is roughly 100 hexes. Even the clans would kill to have that kind of range. But in big stompy robot universe: AC 20 means for IS- Short range 3 hexes, Med Range 6 hexes, Long Range 9 hexes=900 feet, not 3K.

    But for fun reading: Battletechnology 0201 P 25 has what you need.

    Reply
    1. AlphaSaber

      Isn’t there an old quote from one of the original staff that wrote the rules that addresses the range issue? If I remember it right they stated that ranges were arbitrarily set where they are so that the game could fit on a tabletop. Otherwise players would have to rent a warehouse to handle the weapon ranges.

      Reply
  5. Karagin

    I am calling this article out as pure silliness. First off, the author takes the Battletech AutoCannons (ACs) and compares them to the range and damage of real-world artillery.

    Okay bad call, mainly because the ACs are supposed to be the next step of the main tank guns and chain guns we see in real-world tanks and other Armored Fighting Vehicles (AFVs). This means that the entire article is trying to make the claim that the ACs are in fact artillery weapons.

    Second, real-world weapons things working differently than BT. Smaller calibers DO NOT travel as far as larger ones. If it was Battletech claims, then the M4 Carbine with the effective range of 500 meters (roughly 540 yards) would be out ranging 120mm main guns found on most Western AFVs. Sorry pal, not how it works.

    Third, did you even look at the actual information given over the years in the game about AutoCannons? I am really starting to doubt you did. Nowhere are they even remotely described as analogs for real-world artillery.

    And finally, so as to keep this civil and not go off on a rant that would get me banned, Trying to pass off the StrumTiger’s 380 mm RW 61 rocket launcher L/5.4 as the equivalent of an AC20…shows CLEARLY that you didn’t do any real research and should just stop offering up your ideas.

    The AutoCannons ARE NOT artillery, they are main gun equivalents and should be compared to those. Just the Ultra and LB-X and RACs should be compared to Chain Guns and Automatic Cannons

    Reply
    1. Greg Weaver

      I think you kind of missed the salient point: the reason larger caliber AC weapons have less range is that *they can’t be fired with as much force*. Every action has an equal and opposite reaction. In my Army days, I was a crewman on an M728 CEV. Big 165mm, short-barrelled gun. Big 165mm recoil on that sucker, too–the tank weighed 47ish tons fully loaded, and it would still shake like a mofo when that gun fired. That’s with a very low center of gravity and its weight distributed lengthwise on the ground. You try putting something like that on top a 60 ton tower standing 30 meters high, and it’ll fall over.

      And the breech block alone on the L9-patterned XM135 weighed close to 300lbs. The entire gun itself weighed well over 3 tons (can’t find the specific weight online but I remember it breaking a 2.5 ton hoist…), and fired “caseless” (sorta) 65lb HESH charges.

      So to make sense of the Autocannons in Battletech, and to prevent them from being OP across-5-maps-sniper weapons, they’d need to have reduced propellant to both reduce recoil and chamber pressures.

      Also, y’know, it’s just a game. Pew-pew. “We can make fusion engines but lost the knowledge to make basic missile targeting systems, and no one has figured out how to reinvent them.”

      Reply
      1. Karagin

        I am sorry but let’s look at real-world ballistics a bit. A 25mm shell is not going to go as far as a 120mm shell. Yet this article claims that is not the case. Also, let’s look at the game history, the Autocannons from the days of Battledroids, you may recall that was the original game and name, through even this newest edition continue to compare them to current-day main tank guns.

        Now tell me where in the write-ups from the glossaries in the back of the novels or sourcebooks or even the tech readouts up to the main rules of the game does it say the autocannons are equivalent of real-world artillery pieces?

        You were a crewman on M728 that has a gun designed to bust bunkers and obstacles, and you still want to tell me that it’s the same as 120 mm L/44 M256A1 on the M1A2 SEP? And you are going to say that the Autocannons are equal to that 165mm gun that had a single role and purpose?

        I have spent 15 years around the Abrams, both supporting them and in them, I am sorry but your idea in trying to support the original article is insane and sounds more of a friend of the author trying to back them up. The ranges are nerfed we all know that, but at the same time, the autocannons are still the equivalent of main tank guns.

        If we use the logic of the OP, then all the Battletech small arms should have longer ranges and the plain old mech machine gun should have the same range as the AC2. I suggest that the author needs to either revise the article or take it down.

        Reply
        1. Gutfelden

          Hi! I still think that you are missing the argument the author is trying to make, the author does not claim that a 25mm shell will go as far as a 120mm shell. He communicates in the article that weapon systems with high ballistic performance will not only weigh more but also take up more space and produce more recoil. Therefore it is hard to fit a high performance 150mm repeating autocannon into a 55 ton 14m tall machine and much simpler to take that 150mm autocannon shell, and essentially miniaturize it.

          I think a good example of this would be the Barret .50 Cal and the Desert Eagle. These are both semi-automatic weapons that fire a .50 caliber projectile, but one of these is both heavy, large, and has exceptional ballistic performance, while the other fits in the hand (for the most part), and still delivers the punch of a .50 cal but in pistol format. What we know about these two firearms is that they shoot a .50 cal projectile, but one is .50 bmg and the other is .50 ae, both with vastly different performances but for all intents and purposes still a .50cal weapon system. And yes! The 120mm cannon from an Abrams MBT will shoot vastly farther than a 25mm from say… oh a bushmaster, but what if that 120mm projectile was shortened, has less propellant, is fired from a shorter barrel, in a weapon system designed to provide high volumes of destructive power with a high fire-rate? Then this 120mm weapon system may very well have less ballistic performance over distance than the 25mm bushmaster, just as 7.62 NATO will fire farther and more accurately over distance than .50 AE will.

          I think this is how the author of this article is trying to communicate this and I hope this helps clear things up! Also we have to keep in mind that Battletech is a Tabletop Wargame, and the writers have specifically stated and acknowledged that for the purposes of this game some of the weapons and their ranges may not seem realistic to very much include machineguns.

          Reply
  6. TinBane

    In my head-canon, the range issue is targeting.
    All mechs have ECM etc, hence engagement ranges are lower. AC20s on average might be slower than AC2s, hence need better tracking data, so ecm has more impact.

    At the end of the day it’s an abstraction. Probably better to approach it from a balance and flavour ange :)

    Reply
  7. Lily of Sangvis Ferri

    CGL has gone on record saying the ranges on BT weaponry is for game balance and not reflective of what the weapons’ actual ranges would be…

    “Catalyst Games, the present owners of the license, have kept the Hex and range measurements, but have gone on record saying that BattleTech Weapons are really not that short-ranged. The official rationale used is that a) at actual, real-world ranges, a typical playing field would have to have at least 7 mapsheets laid end-to-end, and b) that sort of a game would not be particularly fun, as it would negate tactical movement and physical combat and other dramatic moves in favor of what would essentially be a sniper’s duel.”

    (Swear I pulled that from somewhere here on Sarna originally but that was a few months ago, for just now I pulled this from a screencap on a Discord server for a BT campaign.)

    Reply
  8. Chaosticket

    Good article but it doesnt address the game balance.

    Autocannons are limited to an archaic manner where the higher caliber have to be short ranged, snub nosed, low velocity Howitzers.

    Artillery get it better. Thumper artillery are something like 105mm artillery guns. Marksman artillery are closer to 150mm artillery guns. Long Tom artillery are probably 200-400mm cannons, usually mounted on massive land vehicles, trains, and dropships.

    Battletech does not have realistic weapon ranges for better or worse. Its just a general fault with Tabletop Wargames that they cant actually show the battlefield or else the boards would be parking lots.

    Reply
  9. Beemer

    My headcanon is the same as some others here with battlefield ECM causing targeting issues, thus shortening the effective ranges of many weapons systems. I think CGL stated in the Forward section of one of the rulebooks that weapon ranges are far longer than what’s represented on tabletop, but truncated for ease of play. How many people have a tennis court available to play a company-on-company BattleTech game with realistic ranges? XD

    Thank you for the article, Sean, I enjoyed it! My favorite part of it though is the picture of the Hunchback at the very top. Looks like the pilot experienced a major gunnery skill failure! =D

    Reply
  10. Cupra

    I get the “smaller ACs have longer ranges than larger ACs” point. Its a good one actually.
    But lets be honest, the ranges itself are just wet ’80s techdreams without real reference. A “long range” missile who cant reach 1km (lets ignore super extreme range stage X experimental rules for a sec)? Machineguns (mounted!) who cant hit s**t at 100m?

    Trying to explain BT rules with real life tech/physics makes your brain melt, sooner or later. Dont do this.
    And now go on and play some introtech games with a lance of jagermechs to repent your sins.

    Reply

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