Impact crater of a gauss rifle

[DevianID]

Howdy.  I saw some cool impact calculators online that could input a meteor of .155 meters radius/.31 diameter at the density of iron.  This gives a nice kg weight of 125 kg.  A nickle iron might be more dense more with a smaller radius, not sure, so I just used 125kg of iron as a known value.

I used a speed of 1750 just cause I don't know how fast gauss are supposed to go, but thats roughly mach 5 so worked for me.  And at a 10 meter wide crater already I don't want to imagine faster speeds!

Anyway, the craters were 10 meters wide!  More depending on the surface makeup.  Gauss rifles are heavy slugs indeed!

At a 90 degree angle it was 16 meters wide, at a skipping 5 degree angle it was 7 meters wide and presumably a longer trail.

Imagine what it looks like behind the target when a Thunderhawk misses!  No wonder they can deforest an area haha.

If anyone else wants to play with things, I used
https://www.eaps.purdue.edu/impactcrater/crater_c.html

[Church14]

Your speed is off by orders of magnitude. You can probably just use iron for a density as I think gauss shots are supposed to have a ferrous core. At the speed we are talking about, whatever you wrap it in won’t make that much of a difference.

Gauss rifle is something like 1700 m/s. That site does things in km/s because that how you measure velocities in space (or cm/s for some fields). So the Impact crater is much, much smaller.

[cray]

Gauss rifles are a lot faster than 1700m/s. They have a "long" (20-hex) range in aerospace combat. At 20 x 18-kilometer hexes and 60-second turns, Gauss rifles MUST fire slugs at 6,000m/s, minimum.

However, even a sluggish Aegis WarShip or Behemoth DropShip (both 2/3 thrust) can dodge by 10s of kilometers in 60 seconds. To match the rules' to-hit percentages, Gauss rifles likely have much shorter flight times, perhaps 10-15 seconds. That calls for 24,000m/s to 30,000m/s, minimum.

While aerodynamic drag would slow Gauss rifle projectiles in ground combat at longer ranges, it won't significantly impact muzzle velocity.

The same thinking applies to autocannons, which explains why autocannons are not Tech Rating B. They're much more advanced, hypervelocity weapons than anything that came out of 20th century armories.

[Gladius-XC]

Not quite apples to apples, but the U.S. Navy's railgun fired projectiles at roughly 7400 kph, which is about 2 km/sec (2000 m/s).

[DevianID]

church for the actual site, 1750 m/s was input as 1.75 km/s, so the 10ish meter crater should be good in that way.  I imagine 1750 km/s would punch a hole in the planet, that indeed would be nutty.

Cray, while you are not wrong with 18 km hexes at 60 seconds for 6 km/s, the same ship accelerating at 1g in 1 turn/minute moves 18km 'IRL', but in battlespace they instead move by 36km/2 hexes.  So the space hex math from the gate is wrong--acceleration and hex sizes do not agree.  So I cant take the hex sizes for space at face value for weapons fire--they cant be 18km if 1 G moves a ship 1 hex in 1 minute.  Plus there is other issues with the 1 minute turn scale, like where does the other 5 shots a gauss rifle gets in 60 seconds go?  Its all so undefined.

So Gauss in space would still be faster, but the minimum would be 3000m/s using the acceleration to distance hex scale, instead of 6000.  Still faster then 1750, but unable to be easily defined using the space hexes that dont add up.

Gladius, the navy railgun is quite fast!  Using 2 km/s would only increase the crater size!  Those gauss rifles sure do make a mark!  The navy railgun melts itself firing though right?  So its possible the 125kg watermelon is also partially melted, reducing the impact mass.  I have heard at that speed everything acts like a liquid instead of a solid.

[Maingunnery]

Plus there is other issues with the 1 minute turn scale, like where does the other 5 shots a gauss rifle gets in 60 seconds go?  Its all so undefined.

So Gauss in space would still be faster, but the minimum would be 3000m/s using the acceleration to distance hex scale, instead of 6000.  Still faster then 1750, but unable to be easily defined using the space hexes that dont add up.

You can also reverse the thinking, in that the in atmosphere shots are lower-powered in order to deal with having an atmosphere in the barrel, and with lower powered shots you can easily fire more often.

Gladius, the navy railgun is quite fast!  Using 2 km/s would only increase the crater size!  Those gauss rifles sure do make a mark!  The navy railgun melts itself firing though right?  So its possible the 125kg watermelon is also partially melted, reducing the impact mass.  I have heard at that speed everything acts like a liquid instead of a solid.

Railguns use a different way to accelerate their projectile, so gauss rifles will not have that melting issue.

[klarg1]

At a certain point compression heating will still melt the slug in an atmosphere, but I don’t know how fast it needs to be going for that to be true.

[cray]

Its all so undefined.

It's not undefined. "Each hex on a space map represents roughly eighteen kilometers." --Total Warfare, p. 76. The same paragraph sets a space turn as 60 seconds. They're not linked to thrust points and acceleration, and haven't for 15 years.

Them's the rules, and sets a minimum for muzzle velocity.

At a certain point compression heating will still melt the slug in an atmosphere, but I don’t know how fast it needs to be going for that to be true.

The fantastic, ridiculous Sprint missile (0 to mach 10 in 5 seconds) used an ablative nose cone. Nose temperature in the lower atmosphere was higher than its rocket engine's operating temperatures and exceeded the surface temperatures of some stars.

A thin layer of ablative material wouldn't affect the impact behavior of an autocannon shell or Gauss rifle.

[Daemion]

It's not undefined. "Each hex on a space map represents roughly eighteen kilometers." --Total Warfare, p. 76. The same paragraph sets a space turn as 60 seconds. They're not linked to thrust points and acceleration, and haven't for 15 years.

Them's the rules, and sets a minimum for muzzle velocity.

Longer. AT2 was published in 2000, which TW Aero Rules were copy/pasted from. And that's the stats and rules for that book, as well.

[Daemion]

But!  This brings up an interesting point.  The old Tactical Handbook had a rule for cratering a BT ground hex (digging it out so that it dropped a full 6 meters) at 40 points of damage.  I'm wondering if the higher velocity minimum would reach that scale of earth moving.  Because, if so, then we're looking at 15 to 20 points of damage instead.  Then I wonder why the AC/5 was left off the valid weapons to clear woods hexes with in the old BT 2nd ed rules. 

[General308]

Anyone have TRO2750 handy I might be wrong but doesn't the original 2750 TRO strangle say how fast it shoots?   My old brain could be wrong and I am working so I can't go grab the book and look

[Syzyx]

No, unfortunately. It only says it can 'accelerate a projectile to muzzle velocities twice that of conventional weapon systems'. (TRO: 2750, p. 7)

[guardiandashi]

I also want to say there was some reference that the star league, gauss rifles (10 rounds/ton) were a du/tungsten core, surrounded by ballistic plastics, and with iron driving bands

I always took Natasha's description to Phaelan of it being roughly the size of a melon as being overly simplified as the ballistic properties of cannon balls suck

[JadeHellbringer]

All of this tells me that the old idea of using a Gauss rifle to deliver Elementals to a battlefield is a very bad idea.

[CitizenErased]

All of this tells me that the old idea of using a Gauss rifle to deliver Elementals to a battlefield is a very bad idea.

This just feels like a corollary to Maxim 11: Everything is air-droppable at least once.

[klarg1]

All of this tells me that the old idea of using a Gauss rifle to deliver Elementals to a battlefield is a very bad idea.

It’s fast…

[VanVelding]

All of this tells me that the old idea of using a Gauss rifle to deliver Elementals to a battlefield is a very bad idea.

Not if they hit the target.

I do wonder how many physics-defying conceits are needed to make a setting like Battletech work.


Using just iron (7.874 g/cm³), a perfectly spherical shell (and a diameter of 0.3), and a conservative 6,000 m/sec speed, impact angle of 15 degrees, hitting rock in standard gravity:

Results:
Yield Scaling    0.53 x 101      meters
Pi Scaling (Preferred method!)    1.41 x 101      meters
Gault Scaling    6.88    meters
Crater Formation Time    0.63    seconds

Using the Pi-scaled transient crater, the final crater is a Simple crater with a rim-to-rim diameter of 2.19 x 101 meters.

This impactor would strike the target with an energy of 2.04 x 109 Joules (4.86 x 10-7 MegaTons).


If we ramp it up to nickel (8.9 g/cm³), an oblate with 2/3 the diameter (0.2), and a 30,000 m/sec speed, impact angle of 30 degrees, hitting rock in standard gravity:

Results:
Yield Scaling    1.13 x 101      meters
Pi Scaling (Preferred method!)    2.69 x 101      meters
Gault Scaling    1.61 x 101      meters
Crater Formation Time    0.767           seconds

Using the Pi-scaled transient crater, the final crater is a Simple crater with a rim-to-rim diameter of 4.19 x 101 meters.

This impactor would strike the target with an energy of 1.68 x 1010 Joules (4.01 x 10-6 MegaTons).

Both of those yield craters in the hundreds of meters wide, which is impressive.

[Col Toda]

A gauss slug is 62.5 KG  so crater might be 5 meters at best if that depending on the composition of the ground or mud in question

[JadeHellbringer]

A gauss slug is 62.5 KG  so crater might be 5 meters at best if that depending on the composition of the ground or mud in question

That's also an important factor, good point. Ferro-fibrous armor plating on an assault Mech will almost certainly have a different reaction to a hypersonic slug hitting it than, say, a concrete wall, or a big tree, or a block of ice, or Steve.

...we don't talk about what happened to Steve. Ever see the movie 'Glory'? You know what I mean.

Jokes aside, the effect of the weapon is going to be roughly the same- smack a heavy object at those kinds of speeds into just about anything, and it's not going to be healthy- but just what effect it has is going to vary wildly depending on the surface impacted. Environmental effects like firing through water at a submerged target, gravity variations, and even wind probably would have effects on the damage pattern as well (or at least on your aim!)

[Maingunnery]

A gauss slug is 62.5 KG  so crater might be 5 meters at best if that depending on the composition of the ground or mud in question

Minor correction 1000/8=125 kg, you might be thinking of a light gauss rifle round.

[Charistoph]

Minor correction 1000/8=125 kg, you might be thinking of a light gauss rifle round.

I always hate the assumption that the total weight of the Ammo Bay is only Ammo and nothing else like the material holding the Ammo together or the delivery chain to the Ammo Delivery system.  It may not be the extreme of 50% of the weight you're responding to, but surely more than the null weight you're presenting here.

[Maingunnery]

I always hate the assumption that the total weight of the Ammo Bay is only Ammo and nothing else like the material holding the Ammo together or the delivery chain to the Ammo Delivery system.  It may not be the extreme of 50% of the weight you're responding to, but surely more than the null weight you're presenting here.

One can also assume that the delivery chain is part of the loading system and thus is part of the weapon weight.

[Charistoph]

One can also assume that the delivery chain is part of the loading system and thus is part of the weapon weight.

Well, since Weight of the weapon doesn't increase with the number of Ammo Bays, that's going in the wrong direction.

[Maingunnery]

Well, since Weight of the weapon doesn't increase with the number of Ammo Bays, that's going in the wrong direction.

The loading system of a weapon could be designed with enough capacity for that to simply not matter enough for the abstract.

[Col Toda]

Sadley the precedent from improved One Shot launchers seems the intial feed system is part of the weapon and the extra mass in other ammo slots is the cost of extending that feed system . A one shot missile like weapon is 50 to 60 percent the weight of a full weapon with

an ammo bin .

I suspect for ballistic weapons over 1/2 ton 10 percent of the mass approx is the feed system at a guess  .  So for a Gauss rifle  about 1.5 tons of its mass .  The heavier the ammo round the more mass the feed system eat and the fewer shots per ton their is .

[Charistoph]

The loading system of a weapon could be designed with enough capacity for that to simply not matter enough for the abstract.

It's not the loading system itself that's really in question, its the system that transfers from the Ammo Bay to the weapon's loader, i.e. the feeding system.  A system which can magically transfer from the farthest part in the 'Mech and to multiple weapons on opposite sides of the 'Mech, too.

[Syzyx]

I believe it was Weirdo, but I could be wrong, who logically surmised that everything in BattleTech is liquid which is why such things as the size of cargo bay doors is irrelevant to loading and unloading. Using this discovery it is not very hard to get a feed system that easily allocates to far spread systems wherever they are on a 'mech or other unit.

[Carbon Elasmobranch]

It's not the loading system itself that's really in question, its the system that transfers from the Ammo Bay to the weapon's loader, i.e. the feeding system.  A system which can magically transfer from the farthest part in the 'Mech and to multiple weapons on opposite sides of the 'Mech, too.

At the other end of assumptions, most 'Mechs have two limitations on ammo space - crits, and tonnage. Inner Sphere GRs don't tend to leave much of either to work with. It'd be a really rare design that explored the theoretical limits of GR ammo feed capacity, like it packs every side torso and center torso crit to spare full of shots. At which point it would probably need to start finding room for all the heat sinks that aren't internally stored in the engine anymore.

[MoneyLovinOgre4Hire]

I believe it was Weirdo, but I could be wrong, who logically surmised that everything in BattleTech is liquid which is why such things as the size of cargo bay doors is irrelevant to loading and unloading. Using this discovery it is not very hard to get a feed system that easily allocates to far spread systems wherever they are on a 'mech or other unit.

I've made that joke before, don't know if Weirdo made it before I did.  I've also joked that ammunition in Battletech is stored in a dehydrated state so that each round or missile is the size of a pencil before a single drop of water is added to it when it's loaded into the launcher, at which point it instantly grows to full size.

[DevianID]

I just assume ammo bins being all over the mech is a gameplay abstraction.  Logically it doesnt make sense for the ammo to feed from the left torso, past the engine, into the right torso, when space is available to NOT do that, on things like the marauder and hunchback.  The ammo is 'someplace', probably the most logical place, and the 2d flat record sheet doesnt model a 3d space on a mech anyway, so its just abstract.
Same with how you can put all the ferro extra crit slots on the right arm and torso, but the resulting mech doesnt have a giant bloated right arm and a real skinny left arm using none of its crit slots.  The arms look more or less the same despite one having, for example, 4 heat sinks in it and the other having nothing.