Why do Autocannon have a minimum range?

[Zombyra]

I mean, I know the game reason autocannons have a minimum range, I guess; balance the weapons--blah, blah, blah--long range has a penalty--blah, blah, blah.

But honestly, I'm more of a fan of the fluffy reasons for stuff, and I don't want to kill too many catgirls--because I do love them so--nevertheless I at least want to know the going excuse, if not an actual reason for this.

I understand PPC's i think--energy focus; something about feedback, whatever.  And LRM's--arcing missiles, yeah, ok.  But autocannons? All I can think of is sure it's got to be a long barrel on that gun--but it's not that long of a barrel, and it's not any worse off than the large lasers mounted out on the end of those massive arm-looking things.  But for some reason that guy 50 yards out is harder to hit than that guy that's 100 yards out--what? Also, there's alot of variance among the type of autocannon and the applicability of the extent of the minimum range--so my house rule is, AC's don't have a minimum, because it doesn't make any sense.  BUT, I'd still love to hear the explanation--real world, fluffed-out, or otherwise--and maybe I'd even relent a little--maybe.

[Nahuris]

Actually, there was a fluff entry about this that stated it was due to the weight of the AC, which made it difficult to do subtle aiming corrections.... but never bothered explaining then why the 14 ton AC/20 didn't have minimums, but that the 6 ton AC/2 did.....

I just consider it one of the quirks of battletech and just play the game...... although AC's without minimums would be interesting..... it would make a 3025 Blackjack, or Jagermech more interesting.

Nahuris

[George_Labour]

Perhaps it has to do with the issues of bringing a 'mere' super or hypersonic weapon onto the target, getting the targeting solution, pointing the boom stick the right way and firing the weapon in a mostly accurate manner while the firing unit is itself trying to not get shot.

This would especially hold true with (bipedal) mechs as their humanoid nature works against them in this instance.

If you don't stop to think about it to closely those are almost plausible enough to explain away the matter.

[cray]

They're not weapons meant for point-blank engagements. Barrels too long, aiming adjustments too slow, whatever - some guns and missiles don't do well at point blank range. Consider using a long rifle like an M1 Springfield in a close-quarters, indoor furball against folks with compact machine guns.

And there's the example of the USS Samuel B. Roberts, which actually got so close to much larger Japanese cruiser Chokai that cruiser couldn't shoot the Roberts.
http://en.wikipedia.org/wiki/Battle_off_Samar#USS_Samuel_B._Roberts

[monbvol]

Except that doesn't really work when the same actuators/turret drives have no trouble moving around bigger and heavier weaponry without applying minimum range penalties and Battletech is certainly capable of a much better field of fire than the Chokai which had that particular problem more because of turret and mounting design than the guns themselves.

Fusing problems from too high of a muzzle velocity doesn't make sense either because some ACs are using pure kinetic impactors and those don't keep getting faster after they leave the barrel.

So yeah I too eliminate the minimum ranges on top of all the other things I do for ACs.  Yes I include Gauss Rifles in that but to balance those out I cause them to generate a lot more heat and behave like Plasma Rifles on vehicles(needing power amps if ICE and needing heat sinks).

Everything else is easier to understand from their fluff explanations even if I think the game mechanics go about it in the wrong way sometimes.  PPCs I can understand the field inhibitor causing a delay in the charge build up of the PPC causing a delay between trigger pull and firing that causes accuracy issues close in so that one is fine as is.  LRMs from what I remember are due to the fuses not always arming before hitting the target because they fly so fast.  Reasonable enough explenation but poor execution there.  It'd be easier to go with that if it were a penalty to the cluster hit chart rather than a penalty to hit.

[Lord Cameron]

I mean, I know the game reason autocannons have a minimum range, I guess; balance the weapons--blah, blah, blah--long range has a penalty--blah, blah, blah.

But honestly, I'm more of a fan of the fluffy reasons for stuff, and I don't want to kill too many catgirls--because I do love them so--nevertheless I at least want to know the going excuse, if not an actual reason for this.
sense.  BUT, I'd still love to hear the explanation--real world, fluffed-out, or otherwise--and maybe I'd even relent a little--maybe.

Think about a 100 or 120 mm gun, it can target tanks or inf at some distance out.
But try to hit a moving target at 20 or 30 feet away? Not so easy.

A target moving the same speed but at a much closer distance has a much greater relative movement as seen from the shooter

[beachhead1985]

so my house rule is, AC's don't have a minimum, because it doesn't make any sense.  BUT, I'd still love to hear the explanation

that is a very common house rule in my experience

[Nikas_Zekeval]

I believe one of the early novels fluffed it as longer range ACs had long barrels for accuracy, and couldn't turn them as fast in close engagements.  The AC/10 and AC/20 were relatively shorter barrels, and thus handier to turn.

[I am Belch II]

Because some weapons just have issues. Like the parachute on the Heavy Gauss Rifle!!!

[SCC]

The guns are set/designed for long range engagement, you can't change that in a 'Mech on-the-fly, CV's in theroy

[Jellico]

Except that doesn't really work when the same actuators/turret drives have no trouble moving around bigger and heavier weaponry without applying minimum range penalties and Battletech is certainly capable of a much better field of fire than the Chokai which had that particular problem more because of turret and mounting design than the guns themselves.

Fusing problems from too high of a muzzle velocity doesn't make sense either because some ACs are using pure kinetic impactors and those don't keep getting faster after they leave the barrel.

So yeah I too eliminate the minimum ranges on top of all the other things I do for ACs.  Yes I include Gauss Rifles in that but to balance those out I cause them to generate a lot more heat and behave like Plasma Rifles on vehicles(needing power amps if ICE and needing heat sinks).

Everything else is easier to understand from their fluff explanations even if I think the game mechanics go about it in the wrong way sometimes.  PPCs I can understand the field inhibitor causing a delay in the charge build up of the PPC causing a delay between trigger pull and firing that causes accuracy issues close in so that one is fine as is.  LRMs from what I remember are due to the fuses not always arming before hitting the target because they fly so fast.  Reasonable enough explenation but poor execution there.  It'd be easier to go with that if it were a penalty to the cluster hit chart rather than a penalty to hit.

Weight is part of the equation but also shape.
If you have ever watched Olympic Archery you will notice the strange long pieces of metal in front of the bows. They are basically weights. By putting the weight at the end of a long stick they increase the amount of force needed to rotate the bow around the pivot that is the archer's wrist. This effectively stabilises the bow. The longer the sticks the lighter the weights need to be.

Same applies with rifles. A rifle intended for long range shooting will often have a heavier barrel. Especially if the shooter doesn't have to carry it on foot much.

Now as has been noted above, if light autocannon have long barrels and heavy autocannon have short barrels the 'Mechs actuators could well require more effort to rotate the lighter weapons.

[A. Lurker]

Anime physics -- the same reason smaller-caliber ACs have a longer range than their bigger cousins in the first place.

If you look at an AC/2, it probably has a fairly long barrel relative to its tiny caliber (if it was too short, it would magically lose five and a half tons of weight and turn into a machine gun :) ). Thus, it looks as though it should be shooting farther and be harder to maneuver than the relatively short-and-stumpy AC/20...and thus, in BattleTech, it does.

[monbvol]

I get the principle but as I said before Battletech obviously has actuators capable of moving more weight and longer barrels than an AC-2 without generating a minimum range for it.

[cray]

Except that doesn't really work when the same actuators/turret drives have no trouble moving around bigger and heavier weaponry

I don't agree with that argument. Weapons are not built with the best of everything for every situation. Designers often make compromises to help weapons excel in one area at the expense of others.

Yes, awesome, some large BT weapons aim quickly and easily at point blank ranges because they were designed to do so. That doesn't mean the same actuators were carried over to longer-ranged ACs. The longer-ranged ACs were optimized for longer ranges, with associated compromises in point-blank performance. Be it their targeting, actuators, long barrels, or something else, they were compromised to excel at longer-ranged combat. Sticking with the Chokai...

without applying minimum range penalties and Battletech is certainly capable of a much better field of fire than the Chokai which had that particular problem more because of turret and mounting design than the guns themselves.

...By your own logic that shouldn't happen to the Chokai because there are other proven, centuries-old mountings for cannons that allow ships to rake the waterline. Because of such guns, clearly the Chokai should've been able to shoot any ship at any angle along side it. If we're to follow your logic, the Chokai has no excuse for being unable to shoot the Robertson. Its cannons should've been on the old, proven pintle mounts with excellent arcs of fire.

But those mountings have problems of their own, don't they?

I get the principle but as I said before Battletech obviously has actuators capable of moving more weight and longer barrels than an AC-2 without generating a minimum range for it.

At the expense of long-ranged performance. The actuators ABLE to move AC/20s rapidly to target short-ranged threats are clearly unsuited for aiming at long-ranged threats. Look at the poor long-ranged performance of the AC/20.

[monbvol]

And yet an Arrow IV in direct fire mode has no minimum range and that is certainly a more unwieldy weapon in close.  Sure you have to put it in a turret but the even bigger Long Tom has no trouble firing in close.  Even if we discount those because they operate differently than standard ACs I'm still not entirely sold on the idea since the same mountings have considerably little trouble tracking an ASF at high altitude moving at several times the speed of sound or swinging 3 AC-2s a minimum of 180 degrees in less than 10 seconds.

Like I said I understand the principle.  It is just how everything else meshes and the implications they create in the process.

[A. Lurker]

And yet an Arrow IV in direct fire mode has no minimum range and that is certainly a more unwieldy weapon in close.  Sure you have to put it in a turret but the even bigger Long Tom has no trouble firing in close.

Barring a pointblank shot from a hidden artillery unit (i.e., basically the target stepping right in front of your barrel), you can't make a direct-fire artillery attack against anything within six hexes at all (TacOps p. 185).

[Zombyra]

I think this has been a great discussion to this point, so I wanted to thank everyone for putting in  :-*

When I saw this:

I get the principle but as I said before Battletech obviously has actuators capable of moving more weight and longer barrels than an AC-2 without generating a minimum range for it.

I thought about coming back with the question: Everything gets mounted in the same places; why don't erLL and erPPC's have a minimum range then?  They're big and heavy and shoot a long way, even farther than the autocannon, honestly.  I almost came back with that question.  But then I remembered somebody said this:

Anime physics

A. Lurker, you've got to be some kind of a genius, really. 

In Anime, laser guns kick back, don't they?  Usually with a big circle of ambient energy, possibly pushing back your giant robot and creating a corridor of dust stirred up by the energy wave  :)) 

And because already somebody had said this:

And there's the example of the USS Samuel B. Roberts, which actually got so close to much larger Japanese cruiser Chokai that cruiser couldn't shoot the Roberts.

(I'm familiar with the engagement, an old hobby of mine)
and this:

If you have ever watched Olympic Archery you will notice the strange long pieces of metal in front of the bows. They are basically weights. By putting the weight at the end of a long stick they increase the amount of force needed to rotate the bow around the pivot that is the archer's wrist. This effectively stabilises the bow. The longer the sticks the lighter the weights need to be.

(but I've never even seen olympic archery)

I started to fear for my catgirls.  Because while I want to think about a real world explanation, I still dearly love my catgirls.  And because I love them, I must acknowledge that this . . .

I get the principle but as I said before Battletech obviously has actuators capable of moving more weight and longer barrels than an AC-2 without generating a minimum range for it.

. . . is still essentially correct.  Size and motion and weight really get swallowed up by the whole--giant-stompy-robot-warrior lover in me.  Except at literally-kicking-you-in-the-face-point-blank-range, I don't think the size of the barrel really matters in that it's not the principal cause of the problem.  And I don't think it's relative motion.  If that were true every weapon mounted on a mech would have the same problem with sweeping their weapons in close quarters.  If it's just the aiming, a closer target is also a relatively bigger target, and the speed of target is already kind of swallowed up by the to-hit-mod.  It's not that they're bad explanations or something like that--I've heard some of them before--but it's unsatisfying somehow.  I know: tough cookies, eh?

Nevertheless all this prompting got me to thinking a little more closely about precisely what exactly an autocannon really is.  Isn't is really more like an automatic or assault rifle? (I mean as opposed to the rotary style cannon on an A-10 Warthog)  I seem to remember from the fluff somewhere: variable calibers, variable number of rounds.  That AC5 might be putting out 10 rounds--which because they aren't calculated as discreet units--deal 5 damage.  The AC20 might be putting out 10 rounds or 50 rounds depending on the caliber of the weapon; it just deals 20 damage when you hit.

Lasers really don't kick back.  But an automatic rifle has a problem I can relate to--climb.  When you fire in auto-mode the weapon trys to travel on you--simply put, and for the purposes of my explanation, it has a kick which makes the next round inaccurate--unless you compensate by pulling the weapon down.  There are even assault rifles that are designed to fight climb or have design features to make the weapon climb neutral in auto mode.  And if that's how autocannon are modeled, I think I might have a good explanation.  (With thanks again to everyone)

Someone what knows something about ballistics should probably stop me, but see if I've got some good fluff here:

When you fire an autocannon, you let lose with a 'round' that is essentially a preselected clip of several large caliber, high energy projectiles that go pouring out of a barrel, really fast. The pressures and energies are huge, even for a giant fusion powered robot to handle; the necessity that internal to the cannon are auto-stabilizers designed to fight the 'kick' generated by each round as it leaves the barrel.

The internal stabilizers are designed to account for the battlemech in motion--and against the kick of the magazine of whatever caliber--no matter the number of rounds.  Heavier autocannons are designed with higher grade and much heavier stabilizers, since these weapons are designed for close quarters fighting.  Lighter autocannon are designed for finer adjustments at longer ranges; their internal stabilizers aren't designed to compensate for the faster momentum changes required to follow a target during firing in close range combat.

It's not an aiming problem--it's a during-the-firing-of-this-weapon problem, like the lrm's and ppc's.  It's kind of fluffy too, that's why I like it.  Today at least, this seems to me like a pretty satisfying explanation as it also makes some sense out of a quirky little issue: how come an lbx or ultra 10 which fires at the same range as an ac5, the 10 doesn't have a min?  And while you 'could' theoretically design an AC2 with heavier stabilizers for close range combat, for whatever reason the battletech universe doesn't demand them.  The four sizes of autocannon represent a range of calibers and designs that are fluffed out to be the optimal mix of caliber, range, and weight; it's what manufacturers design around, and it's what customers want--for whatever reason.

Of course I'd be shocked to find out this is a good answer; I'd still like to encourage more brainstorming!
 [watch]

[Blackjack Jones]

Well Zombyra, keep in mind that lasers and heat weapons are the only two "families" of ranged weapons that don't have a black sheep with minimum range in them.
The problems with tracking/recoil/minimum safe distance/etc. extend to ballistics, missiles, and PPC's in various capacities.

As for lasers themselves, there's a pretty good argument to say any "barrel" past the focusing lenses is just there in a protective (or aesthetic) capacity, so they aren't as heavy
or unwieldy as a barrel of a ballistic weapon. And with the proper focusing/aiming gear, a laser's target doesn't necessarily need to be on the centerline of the complete weapon assembly,
as you don't need to maneuver the power generation gear, just the focusing assembly and lenses. A ballistic weapon needs to line up everything from the breech to the end of the barrel.
This can translate to needing much less time to get a bead on the target for a laser. Or to put it another way: An AC/2 might be trying to aim almost all of it's six tons at a target,
where a Large Laser might only be aiming a ton or two.

For reference see:

http://en.wikipedia.org/wiki/Airborne_Laser
http://en.wikipedia.org/wiki/Advanced_tactical_laser
 
And let's have a look at Gauss weapons for a minute: except for Magshots and APGRs, every vehicular class Gauss weapon has a minimum range of some kind.
We know Gauss weapons are more efficient than AC's from a power to weight ratio, so even if they didn't have tracking problems, recoil is apparently still a problem.

[Nikas_Zekeval]

I get the principle but as I said before Battletech obviously has actuators capable of moving more weight and longer barrels than an AC-2 without generating a minimum range for it.

It's not just mass, but how it is distributed.  Everything has a moment of inertia, which represents how hard it is to turn, or to stop turning once you start it.

For swinging a rod by it's end (simplified model for a cannon barrel) the formula is I=(mL^2)/3  Or one third the mass times the square of the length.  So the force needed to affect it's rotation is half if you cut the mass in half, but quadrupled if you double the barrel length.  Or doing both and you get something that has twice the moment of inertia.

[cray]

And yet an Arrow IV in direct fire mode has no minimum range and that is certainly a more unwieldy weapon in close.

Alright, monbvol, then please explain the minimum range of BT's ACs. It's easy to sit back and reject any alternative that works but has a contradiction in unrelated weaponry, but why don't you try working from the other side and build up a plausible explanation that fits the rules?

[HavocTheWarDog]

Having served in the artillery thats more of an elevation problem than a targeting problem!

[chanman]

Alright, monbvol, then please explain the minimum range of BT's ACs. It's easy to sit back and reject any alternative that works but has a contradiction in unrelated weaponry, but why don't you try working from the other side and build up a plausible explanation that fits the rules?

AC/2s are actually gyroslug weapons, explaining their low explosive payload, relatively low weapon weight, and ludicrous range. They are simply difficult to use at close range because the propellant is relatively anemic and the booster motor hasn't yet accelerated the projectiles to cruising speed yet.  O:-)

[monbvol]

Alright, monbvol, then please explain the minimum range of BT's ACs. It's easy to sit back and reject any alternative that works but has a contradiction in unrelated weaponry, but why don't you try working from the other side and build up a plausible explanation that fits the rules?

Simple.  I can't explain why they do have a minimum range in a satisfactory way without creating contradictions as to why other equipment doesn't or why different mounting locations don't impact the minimum range.  After all it stands to reason that a Torso mounted AC should have even more difficulty tracking a target in close due to a more confined mounting but it doesn't.  Likewise I can't explain why the minimum range on the AC-2 Carrier's Front mounted AC-2s isn't longer than the Turret mounted AC-2s of the Pike Support Vehicle.

Sometimes something happens in the rules that probably shouldn't.  Fluff tries it's best and sometimes it does offer plausible explanations.  After all Battletech is not a reality simulator but there are some people who certainly know their stuff writing for it.

If Battletech were a better reality simulator oh yeah no problem.  The reasoning is sound.  I do understand it and I do not refute that targets in close are a bit more of a problem for long barreled weapons with our current understanding of mounting techniques and technology.  My problem does stem from Battletech repeatedly demonstrates that it has superior mounting techniques and technology though.

Maybe I am just too hung up on it being a game though.

[stoicfaux]

Ugh, barrel length as the reason?  Really?  That may work for the Shadowhawk or Rifleman, but not for the Wolverine or the Daikyu, and the latter has AC/5s embedded in its forearm, the barrels of which don't extend far enough to even interfere with the hand actuators and thus should be easy to maneuver at point blank range.  The Daikyu's AC5s really are point and click.

Plus, even with the long barrels of the Shadowhawk and Rifleman, any target that's two or more hexes away is definitely not close enough for barrel length to matter anymore, so the long rifle in close quarters battle excuse doesn't hold water either.


Which leaves either ammo or tracking as the culprit(s).

[monbvol]

Ugh, barrel length as the reason?  Really?  That may work for the Shadowhawk or Rifleman, but not for the Wolverine or the Daikyu, and the latter has AC/5s embedded in its forearm, the barrels of which don't extend far enough to even interfere with the hand actuators and thus should be easy to maneuver at point blank range.  The Daikyu's AC5s really are point and click.

Plus, even with the long barrels of the Shadowhawk and Rifleman, any target that's two or more hexes away is definitely not close enough for barrel length to matter anymore, so the long rifle in close quarters battle excuse doesn't hold water either.


Which leaves either ammo or tracking as the culprit(s).

Actually the Rifleman is a great example of why barrel length as the reason why ACs have a minimum range creates a logical disconnect.

Look at the original art work for the base model Rifleman.  Even if we accept that there is independent rotation on the horizontal axis the mounting clearly shows that both weapons on the arm are using the same actuator for vertical rotation.  Even if that assumption is wrong looking at it the mounting clearly is not suited for more than a few degrees of independent vertical rotation which is fine against targets farther away.  So obviously against close targets at different elevations the arm mounted lasers obviously have to contend with the weight of the barrel of the AC and yet they don't have a minimum range in this case.

[BirdofPrey]

Because it's a game and things get done for balance reasons even if they don't make sense.
Also the fluff is much less abstract.  The game would be far too complicated if every mech had a completely unique method of operation.

[chanman]

Gyroslugs. The long period of time they spend accelerating in the barrel means that longer barrels are more adversely affected by sudden movement.

[monbvol]

Autocannons have enough going against them that they really don't need a minimum range on top of everything else.

Rocket assisted makes the most sense so far but I have memories of AC-5s using unassisted kinetic impactors and unassisted shaped charge shells.  I can't really think of any fiction I've read where AC-2s have even come up, let alone what kind of ordinance they use.

[MoneyLovinOgre4Hire]

The only time I can remember AC-2s coming up in one of the novels was in Binding Force when Ares got into a fight with a BJ-1 Blackjack, but the minimum range was never mentioned.

[Nebfer]

Per the fluff Autocannons fire Depleted Uranium tipped High Explosive Armor Piercing ammo.

The easiest way to explain minimum range is likely that it's a mix of reasons. Targeting and tracking may be at fault for some, others it might be weapons configuration, and other ammo types used.

Some ammo types have fuzes that require it to spin so many times before it arms it self, others require elements to fall away before it's main component will work effectively (like a sabot). Some weapons may be configured to hit targets accurately out to a much longer range than others and as such they may have some difficulty hitting targets up close.