31 replies to this topic

[Melcyna]

Fahr, on 09 July 2012 - 08:07 AM, said:

OK - so this is just me examining the ideas behind BT ballistics... The suspension of Disbelief issue that was brought up assumes that the larger AC round has an equally larger amount of propellant AND that the round is doing all it's damage from impact. in other words that the two ACs are firing at the same muzzle velocity.

my assumption was that the small bore ACs were like Magnum .22 rounds, super fast, low mass, not a large amount of damage compared to say a 30-06 - but still effective. they don't do as much damage, but the rounds get there faster, while the Large Bore (ac/20) were like shotgun slugs, they are travelling much slower but have much more mass, so they impart more damage. with the AC/5 and AC/10 being more like standard rifles.

we're talking also about the ability to penetrate massive specialized armor with massive slugs, so part of the range reductions were in my mind from air resistance. there is a good reason to not want to carry enough propellant to fire the AC/20 slug as far and fast as the AC/2. all that propellant will go boom if it gets hit.

just because the overall damage inflicted is bigger, doesn't mean that the round is traveling faster - in my opinion.

Unfortunately the two are directly related...

see a slow traveling but large in mass slug is not necessarily going to do more damage than a fast traveling but low mass slug (ie: not carrying more kinetic energy).

in fact the equation is in favor of the faster traveling one (basic physics) given the effect of the velocity is squared... compared to the mass where it's linear, this of course assuming that the projectile is going to do damage through kinetic energy with direct impact.

If the large autocannon, say AC-20 fired some form of slow projectile... then you don't need large propellant to do it... since the equation favor speed over mass and whatever kinetic energy the projectile is going to have you have to impart to it through the propellant (unless if it carry internal propellant ie: rocket). You need MORE energy (more propellant) to fire something faster, than you do to fire something heavier proportionally... so in order for the AC-20 to justify it's massive size and weight would logically entail that it has a massive energy transfer to the projectile (necessitating a large and heavy gun assembly to withstand the pressure), else otherwise if the projectile is a low velocity projectile... then all the extra weight and bulk on the gun is not necessary at all, the caliber may be larger, but a low velocity gun can be made much thinner and lighter compensating the caliber size.

Edited by Melcyna, 09 July 2012 - 09:45 AM.

[Schtirlitz]

I want homing cluster ammo

[Fahr]

Melcyna, on 09 July 2012 - 09:44 AM, said:

Unfortunately the two are directly related...

see a slow traveling but large in mass slug is not necessarily going to do more damage than a fast traveling but low mass slug (ie: not carrying more kinetic energy).

in fact the equation is in favor of the faster traveling one (basic physics) given the effect of the velocity is squared... compared to the mass where it's linear, this of course assuming that the projectile is going to do damage through kinetic energy with direct impact.

If the large autocannon, say AC-20 fired some form of slow projectile... then you don't need large propellant to do it... since the equation favor speed over mass and whatever kinetic energy the projectile is going to have you have to impart to it through the propellant (unless if it carry internal propellant ie: rocket). You need MORE energy (more propellant) to fire something faster, than you do to fire something heavier proportionally... so in order for the AC-20 to justify it's massive size and weight would logically entail that it has a massive energy transfer to the projectile (necessitating a large and heavy gun assembly to withstand the pressure), else otherwise if the projectile is a low velocity projectile... then all the extra weight and bulk on the gun is not necessary at all, the caliber may be larger, but a low velocity gun can be made much thinner and lighter compensating the caliber size.

but you are still equating damage (the 20 part of the AC/20) to caliber, it is a massive gun, with high damage and short range, much like firing slugs from a shotgun, high damage, short range, versus firing a fast small projectile for high range small damage, that was how I always thought of it, when you reach the middle ground, the trade is for a little more punch at lower range vs a little more range for less punch - I think of it like different types of guns serving different roles. ie they designed it that way.

I know that if you keep the mass the same and vary the propellent, faster == more hitting power, but that is a balance in the design, I am suggesting that firing the AC/20 sized slug at AC/2 ranges would reguire an even heavier gun to handle the pressures in moving such a huge slug so fast, and would of course do much more damage because faster == more kinetic energy when the weight is the same.

So - just like in modern guns, you design the guns for different things.

the question becomes why design them like that?
AC/20 and freindly fire - if that massive slug was travleing as far and fast as an ac/2, then you run a much greater risk of hitting an ally with it and destroying them completely. a stray ac/2 is unlikely to do that. so you design precision long range munitions and massively powerful short range ones - that way you don't have as much risk of shooting your freinds with the uber deadly ones - where accuracy is likely to be the least (furball range) and low damage but very acurate for sniping ranges where you can make every hit in the same location.

it seems reasonable in game to design them that way - to me.

(done hijacking - laters)

[wanderer]

Buck Rogers, on 08 July 2012 - 11:59 PM, said:

Something that never, ever made any sense to me, is that while the LB-10X AC is a shotgun...

It has significantly more range than the AC-10! Sub-caliber rounds have much greater range if they're in a sabot or something like that, but not in a shotgun!

If the shell doesn't split into submunitions until it gets proximity, it'd work fine. Like a flak round, basically.

Otherwise, in tabletop it'd lose damage potential with range, due to the submunitions spreading out further as the range was extended.

[Melcyna]

Fahr, on 09 July 2012 - 10:18 AM, said:

but you are still equating damage (the 20 part of the AC/20) to caliber, it is a massive gun, with high damage and short range, much like firing slugs from a shotgun, high damage, short range, versus firing a fast small projectile for high range small damage, that was how I always thought of it, when you reach the middle ground, the trade is for a little more punch at lower range vs a little more range for less punch - I think of it like different types of guns serving different roles. ie they designed it that way.

I know that if you keep the mass the same and vary the propellent, faster == more hitting power, but that is a balance in the design, I am suggesting that firing the AC/20 sized slug at AC/2 ranges would reguire an even heavier gun to handle the pressures in moving such a huge slug so fast, and would of course do much more damage because faster == more kinetic energy when the weight is the same.

So - just like in modern guns, you design the guns for different things.

the question becomes why design them like that?
AC/20 and freindly fire - if that massive slug was travleing as far and fast as an ac/2, then you run a much greater risk of hitting an ally with it and destroying them completely. a stray ac/2 is unlikely to do that. so you design precision long range munitions and massively powerful short range ones - that way you don't have as much risk of shooting your freinds with the uber deadly ones - where accuracy is likely to be the least (furball range) and low damage but very acurate for sniping ranges where you can make every hit in the same location.

it seems reasonable in game to design them that way - to me.

(done hijacking - laters)

friendly fire wise, that made no sense given that they have no qualm with gauss rifle... or PPC or hell a long tom. One would be hard pressed indeed to argue from that angle in favor of the shorter range given there are a myriad other ways to avoid friendly fire than purposely stunting your very own weapon under such ridiculous premise.

And again back to the caliber and damage, why does the AC-20 inflict massive damage if it's supposed to be a slower velocity projectile? Or why design it such at all if damage is the intention?

Like i said, the equation clearly favor speed over mass, given the velocity is squared... while the mass is linear.

Or put it another way, it made no sense to use the heavier slower slug if the intention is to do damage since you can better improve the amount of energy you transfer into the projectile by making it faster rather than making it more massive.

To put this in an example:
since the velocity is squared and the mass is linear...

i can produce the EXACT energy content in a projectile that is 4 times lighter than an AC-20 slug, by simply firing this lighter slug at twice the speed.

same energy, 4 times less massive slug... and not to mention that since the slug is going to be twice faster, it'll be easier to aim at moving target too should that be an issue.

Edited by Melcyna, 09 July 2012 - 10:46 AM.

[Deadmeat313]

Melcyna, on 09 July 2012 - 01:04 AM, said:

heavier mass projectiles retain their momentum a lot better overall than lighter ones except in cases where the drag overshadow the kinetic energy.

What is this nonsense?? Everybody knows that range decreases in proportion to calibre! To get the longest range cannon you need to make the shells as small as possible.

[Uri Brauer]

KageRyuu, on 09 July 2012 - 02:22 AM, said:

...hopefully the AC will get access to it's special munitions.
http://www.sarna.net...ecial_Munitions

Hmm. Mostly useless in MWO, and AP is stupidly overpowered. So, no.

[CaveMan]

This discussion about the range of autocannons is overlooking some things. I'll attempt to explain.

1) The range of autocannons in BT has nothing whatsoever to do with muzzle velocity. The MV of an AC/2 and an AC/20 aren't that much different. The primary reason the AC/20 has a shorter effective range is twofold.

First, AC/20s fire a burst(1) of shells whose total weight is more than 100 kilograms (possibly up to 180), with a caliber between 75 and 205 millimeters. A little basic math tells us that these shells are therefore long, and correspondingly unstable when fired from the AC/20's stubby(2) barrel (an ideal bullet is short, wide, and spun at a high RPM). The AC/2, firing 10-20 kg of shells in a caliber between 30 and 75 millimeters, from a much longer barrel, produces much more stable projectiles. The AC/20's enormous shells start to yaw and tumble over a relatively short distance, which dramatically reduces its accuracy over long ranges.

Second, recoil is an issue. Although it might seem counter-intuitive, autocannons are not hard-mounted to the 'Mech's chassis. If they were, firing the gun would cause the 'Mech to fall. (Imagine firing an elephant gun. Now imagine firing an elephant machine gun. You get the picture.) Even for a 100-ton 'Mech, the weight of a single AC/20 shot is a significant fraction of the machine's mass. It would be equivalent to a 200 lb man firing a gun whose bullet weighed almost half a pound.
So a large chunk of the weight of that autocannon is a hydropneumatic recoil compensator system. The gun basically "floats" on a shock absorber. Recoil is transferred to a working fluid, which compresses a gas, and then a valve relieves the pressure on the system, transferring the recoil energy (and a lot of heat) to the air. These systems are pretty effective, but they can't eliminate all the recoil, because nothing is 100% efficient.
So a certain amount of that recoil goes into knocking the gun, and therefore the 'Mech, back. This recoil throws off the weapon's aim, making it difficult to keep all the shells on target.
The more powerful the autocannon, the stronger the recoil. The AC/20 is thus proportionally affected more than the AC/2, and its shells spread out wider, making it difficult to score an effective hit at long range. An AC/2's shells might all fall within a 1-meter circle at 720 meters, but the AC/20 has the same spread at just 270 meters.

2) Most autocannons are not firing solid bullets₍₃₎. The standard autocannon round is a HEAP (High-Explosive Armor Piercing₍₄₎) round that consists of a shaped charge propelling a wad of molten copper, osmium, or some other dense, flexible metal to hypersonic velocities.
The actual muzzle velocity of the projectile (1000-1500 m/s) is insignificant compared to the explosive velocity of the shaped charge (10,000 m/s or so). Bigger shells are more important for damage than faster ones.
Why are HEAP rounds used and not solid penetrators? Because BattleMech armor is a fantastic energy absorber₍₅₎. No autocannon carried by a 'Mech could produce the velocities needed to penetrate heavy armor without using shaped charge ammunition. It took Gauss rifle technology for solid shot to become viable against 'Mechs again. Thus to inflict more damage, they started making bigger and bigger explosive shells, until 'Mechs were lobbing almost a quarter ton of shell at one another.
To produce a viable 'Mech-scale weapon capable of producing that sort of firepower, they had to make sacrifices in accuracy, and that's why more damaging autocannons have shorter range.₍₆₎

Spoiler

1AC/20s mentioned in the sourcebooks are said to fire anywhere from 1 to 10 shells at a time, so the "average" AC/20 is probably firing 4-5 in a burst.

²The barrel length in calibers gets shorter with each class of autocannon because of barrel heating and weight issues. Shorter barrels can't effectively spin a projectile to the same RPM as longer barrels, because excessive rifling twist can cause the projectile to become stuck, or fail to engage the rifling at all.

³There are a few autocannons mentioned in sourcebooks that are said to fire solid depleted-uranium projectiles. The sourcebook authors probably just used "depleted uranium" because it sounds cool and is used by weapons like the GAU-8 Avenger and Rheinmetal 120mm.

⁴The same thing as today's HEAT rounds, but with a name change since they're designed to be used against more than tanks.

⁵A Gauss rifle inflicts between 500 and 700 megajoules of kinetic energy to the target. That's roughly the same energy as a 500 lb Mk82 aerial bomb exploding. That kind of destructive power would reduce any modern-day tank to a smoldering wreck. Even the humble AC/2 has 2-3 times the firepower of today's most powerful tank guns, and even the lightest 'Mech can survive several hits from one.

⁶The real reason, as we all know, is game balance. If AC/20s had the longest range of any autocannon, no one would use anything else.

EDIT: Sorry, that wasnt supposed to be a TL;DR post. I just get carried away.

Edited by CaveMan, 09 July 2012 - 01:49 PM.

[Melcyna]

Hmmm, that's a better attempt of explanation on their lore.

unfortunately it opens more new holes.

For example if they are attempting to lob HEAT shells at each other with AC then logically you'd want to concentrate that HEAT shells impact on a single location rather than firing bursts of it at a random firing spread cone, ie: they'd just stack the HEAT warheads in a single shell (multi warhead shell, analogous to the tandem, multi warhead HEAT missiles/charge of today) rather than firing bursts of separate HEAT shells and striking multiple separate point and thus achieving no penetration and wasting HEAT warheads on what basically amount to nothing more than eroding ablative armor surface on a wide area.

And second is that HEAT will function with no need for high velocity at all... (hence why they are used in AT missiles, AT charge, etc though we no longer use the last one since the advent of effective portable AT rocket launcher).

IF, they attempt to use HEAT warhead, then it becomes illogical to fire the shell at supersonic speed with large recoil dampeners since the HEAT warhead will function as long as it can detonate in the required distance from the target regardless of how fast you throw the warhead at it.

Obviously they were attempting to use HEAT concept since it sounded cool, but unfortunately in this case it made even less sense to justify their AC design.

Logically then, if the AC fires a sort of HEAT warhead then it's far more sensible to lob a single lower velocity multi charge stacked HEAT warhead, dispensing away with the need for massive recoil dampeners (lower velocity gun have less severe recoil proportionally) and dispensing away with the need to fire a full burst of shells which again reduces the impact of the recoil, which would achieve far better penetration effect and damage and have a much lighter gun assembly to boot.

Deadmeat313, on 09 July 2012 - 11:42 AM, said:

What is this nonsense?? Everybody knows that range decreases in proportion to calibre! To get the longest range cannon you need to make the shells as small as possible.

I assume ur being sarcastic.

[light487]

I think it will be cluster only upon release.. unless you get down to the nuts and bolts of things, the newbie to BT is just going to see the LBX as a "shotgun" and the "AC" as a "machine/mini gun".. of course the LBX is not a shotgun.. but that's how people will perceive in game without any BT background knowledge. Having the LBX with regular rounds won't differentiate it enough from ACs for newbies to understand.. so I think the simple solution here is to just keep LBX's as cluster rounds and ACs are regular rounds..

[CaveMan]

Melcyna, on 09 July 2012 - 07:55 PM, said:

Obviously they were attempting to use HEAT concept since it sounded cool, but unfortunately in this case it made even less sense to justify their AC design.

Yeah. Unfortunately we're stuck with a universe where the technology was designed by sci-fi writers.

_{//says the sci-fi writer....}

[Melcyna]

The problem in particular here is that both HEAT warhead and the weapon utilizing them (ie: AT missile, low velocity gun, tank gun etc) are not uncommon at all, in fact the tech they are based on and the underlying mechanism is quite well known for anyone with interest in military tech.

So anyone with at least basic understanding on how they are utilized in the real world, will immediately see the holes in the explanation.

That they want to provide backdrop for the lore is fine and all, entertaining even...

but in this case, they open up more holes in the lore than they patched....

it probably would've suffice to just give a vague mechanism outlying their function, while avoiding the details and let the audience use their imagination to fill the rest... rather than attempting to utilize concept and mechanism that they don't quite fully understood