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Old 11-29-2014, 09:33 PM   #1
BraselC5048
 
Join Date: Oct 2012
Default Designing an Artillery piece - 3e vs 4e

Anyway, I'm writing up states for a 105mm recoilless rifle, nearly identical to the Watervliet M40 in many ways, but with a counter mass system and a purpose more of firing full size 105mm artillery shells in direct fire than anti tank work.

Which leads to the 3e vs 4e question. Going by GURPS: WWII, a 105 shell does 5dx8 damage (presumably all cr explosive) with 10d shrapnel. Going by High Tech, it's a comparatively puny 5dx5 explosive, with just 5d-1 shrapnel.

The basic problem is that it's being designed for use in an environment (TL 8+^, with as little as possible of the ^), where everybody and his brother in a military environment will be wearing modern body armor, usually around DR 16. So it really needs at least 8d shrapnel to actually injure anybody with it, preferably 10d. It's also likely to be frequently used in a vacuum, where (by my rules) it's 1/2 damage in the hex of the explosion, and divide damage by 8 past that, and 8 again every 2 additional yards. (So 1 yard/hex away would be divided by 8, and 3 by 64!)

(Surprisingly, this combination leads to the use of 8d concussion grenades, which only do 4d in the hex they land in, any pretty much zip past that, but it's better than nothing, since a frag grenade would do far less.)

Going by 3e, a direct fire 105 shell has a decent kill radius from shrapnel, and useful concussion damage (in a vacuum) in a 2 hex radius. Going by 4e, the dropoff rate surprisingly gives the same 2 yard useful radius for explosive damage, and shrapnel damage unlikely to actually put somebody out of action past DR 16 without multiple hits.

So I'd rather use the 3e stats, obviously, since it actually makes shrapnel effective, making it extremely useful for clearing large starship open areas.

Incidentally, the designers of the shell know the rules too, and would rather sacrifice down to 5dx5 crushing in turn for 10d shrapnel damage, or at least 8d, perhaps by controlling the fragmentation and fragment size of the shell.

Perhaps 5dx5 [8d] as a compromise, or maybe 4dx5 [8d]?


Also, one typical target would be an improvised barricade. Generally, it's a pile of crates, boxes and furniture, with a spare 1.5" titanium alloy starship hull plate (I did my homework and ran the engineering numbers) wedged in between them somewhere, or just propped up against the back side. That provides a heck of a lot of DR against bullets, perhaps DR 75, while being able to be thrown together quickly from what's easily at hand. It also can be taken apart by hand just as quickly, by moving the boxes and removing, or just knocking over, the hull plate. There might be a LMG on a bipod on top of it, or a .50 cal HMG on a tripod behind it. My other question is whether it's best to go for some type of airburst fusing, or simply aim for a direct hit (impact fuze). A direct hit obviously would mangle the plate and destroy everything else, and there wouldn't be a barricade there anymore. My question is whether it would kill or injure the gunners behind it, and whether it would also destroy or mangle the MG itself. It's also only 8 ft from deck to overhead, so there's some potential for the blast rebounding off of that (although the overhead will likely have a foot deep layer of a jumble of spare parts hung under it, so closer, but not a smooth surface either, more blast absorbing).

Also, what if they had more time to prepare, and welded the plate to the deck? What would that change?
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Old 11-29-2014, 10:08 PM   #2
Langy
 
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Default Re: Designing an Artillery piece - 3e vs 4e

Quote:
Originally Posted by BraselC5048 View Post
(Surprisingly, this combination leads to the use of 8d concussion grenades, which only do 4d in the hex they land in, any pretty much zip past that, but it's better than nothing, since a frag grenade would do far less.)
Why's that? The primary injury mechanism of a frag grenade (the frags) shouldn't be penalized in a vacuum environment.

Quote:
So I'd rather use the 3e stats, obviously, since it actually makes shrapnel effective, making it extremely useful for clearing large starship open areas.
I'm going to guess this is a higher-TL game than the 1950s when this was actually introduced. Thus, they should be able to design a better type of fragmentation warhead than a ye olde one. I'm not sure where you got the stats for the shell, though - the M40 doesn't have any shells similar to the ones you describe listed in High-Tech.

Quote:
Also, one typical target would be an improvised barricade. Generally, it's a pile of crates, boxes and furniture, with a spare 1.5" titanium alloy starship hull plate (I did my homework and ran the engineering numbers) wedged in between them somewhere, or just propped up against the back side. That provides a heck of a lot of DR against bullets, perhaps DR 75, while being able to be thrown together quickly from what's easily at hand. It also can be taken apart by hand just as quickly, by moving the boxes and removing, or just knocking over, the hull plate. There might be a LMG on a bipod on top of it, or a .50 cal HMG on a tripod behind it. My other question is whether it's best to go for some type of airburst fusing, or simply aim for a direct hit (impact fuze). A direct hit obviously would mangle the plate and destroy everything else, and there wouldn't be a barricade there anymore. My question is whether it would kill or injure the gunners behind it, and whether it would also destroy or mangle the MG itself. It's also only 8 ft from deck to overhead, so there's some potential for the blast rebounding off of that (although the overhead will likely have a foot deep layer of a jumble of spare parts hung under it, so closer, but not a smooth surface either, more blast absorbing).
I'd go with airburst fusing; going around a barricade is usually better than smashing into it. Should be easily doable.
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Old 11-29-2014, 11:06 PM   #3
Ulzgoroth
 
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Default Re: Designing an Artillery piece - 3e vs 4e

I suggested an EFP warhead before. I don't think simple explosives will do what you want, but an explosively forged projectile can 'top attack' as it flies by and is actually good at going through armor...

You also might be able to get a little more concussive power out of your grenades if you allow cutting-edge fillers, like CL20 (found in the High Tech REF table). It looks like nobody actually uses it in weapons yet, but it looks workable.

Also, with the vacuum nerfing blast effects and everyone wearing armor, you could just go with heavier grenades. The TL7 M67 hand grenade (HT192-193) is already 9d, and it only weighs 0.9 pounds and includes some fragmentation casing. You could easily get at least twice that much explosive into a throwable grenade...
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Originally Posted by Langy View Post
Why's that? The primary injury mechanism of a frag grenade (the frags) shouldn't be penalized in a vacuum environment.
Because the frags are pretty much useless against the DR of the armor.
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Old 11-29-2014, 11:16 PM   #4
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Default Re: Designing an Artillery piece - 3e vs 4e

Another thing to keep in mind is that explosive damage, much like strength, in 3rd edition was liner while in 4th it's quadratic. That is in 3rd a 5dx8 blast was 8 times more powerful then a 5dx1 blast while in 4th it's 64 times more powerfull so that "puny" 5dx5 is actually 3 times more powerful then the 3rd damage you listed.
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Old 11-30-2014, 12:15 AM   #5
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Default Re: Designing an Artillery piece - 3e vs 4e

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Originally Posted by Ulzgoroth View Post
I suggested an EFP warhead before. I don't think simple explosives will do what you want, but an explosively forged projectile can 'top attack' as it flies by and is actually good at going through armor...

You also might be able to get a little more concussive power out of your grenades if you allow cutting-edge fillers, like CL20 (found in the High Tech REF table). It looks like nobody actually uses it in weapons yet, but it looks workable.

Also, with the vacuum nerfing blast effects and everyone wearing armor, you could just go with heavier grenades. The TL7 M67 hand grenade (HT192-193) is already 9d, and it only weighs 0.9 pounds and includes some fragmentation casing. You could easily get at least twice that much explosive into a throwable grenade...

Because the frags are pretty much useless against the DR of the armor.
He's not talking about a hand grenade for his big gun. He's talking about a 105mm recoilless rifle firing 25-pound shells (which is one reason I'd like to see where he got his stats from - 5dx5 sounds about right, but I don't remember any rules for frag damage in High Tech, while in Ultra-Tech a 100mm HE shell does 6dx5 cr ex [5d] damage, which is a bit more than he gave it).

In any case, that 4d concussion damage he's talking about will be completely defeated by the DR 16 body armor he's giving them. Thus, for either a frag grenade or a concussion grenade, if that body armor covers the entire body the grenade will do nothing. The frags will still play merry hell if they have no limb armor, though.

Last edited by Langy; 11-30-2014 at 12:20 AM.
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Old 11-30-2014, 12:33 AM   #6
Ulzgoroth
 
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Default Re: Designing an Artillery piece - 3e vs 4e

It might be useful to note that the M40's HESH shell rates 8dx5. That's probably around the maximum concussive power you could get into that round, at least as of the 1950s. A fair bit better than 5dx5!

Fragmentation, frankly, I don't think you can do anything about.
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Originally Posted by Langy View Post
He's not talking about a hand grenade for his big gun. He's talking about a 105mm recoilless rifle firing 25-pound shells (which is one reason I'd like to see where he got his stats from - 5dx5 sounds about right, but I don't remember any rules for frag damage in High Tech, while in Ultra-Tech a 100mm HE shell does 6dx5 cr ex [5d] damage, which is a bit more than he gave it).
5dx5 [5d+1] is right out of the cannon table on HT140. I don't know where you get a 25-pound shell, though. (The 105mm howitzer and 106mm recoilless rounds are listed at 40 and 38 pounds, respectively, but that would be for a complete shot so the shell alone is less.)

As for rules for fragmentation...I don't believe there are any rules stated. However, there is an unstated but extremely consistent rule: fragmentation dice are 1d/20mm of warhead diameter. I have yet to find an exception in any weapon table.
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Originally Posted by Langy View Post
In any case, that 4d concussion damage he's talking about will be completely defeated by the DR 16 body armor he's giving them. Thus, for either a frag grenade or a concussion grenade, if that body armor covers the entire body the grenade will do nothing. The frags will still play merry hell if they have no limb armor, though.
It does seem pretty inadequate, but if you use rolled damage it has a somewhat decent chance of not being entirely useless...
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Old 11-30-2014, 07:13 AM   #7
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Default Re: Designing an Artillery piece - 3e vs 4e

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Originally Posted by Ulzgoroth View Post
Because the frags are pretty much useless against the DR of the armor.
Probably realistic. Some of the feedback on wounds from fragmentation in the port-millennial wars has been that frag wounds stop where armor starts. It's on be reason for the common limb wound problems. In previous wars those same attacks were probably fatalities due to damage to unarmored torsos.

It is not at all unlikely that future combat where everyone (at least on one side) has at least light full body coverage will see a loss of interest in all but the heaviest fragmenting weapons.

Seal the armor and it might even stop enhanced concussion weapons like thermobarics. You could end up in a situation where casualties have to be inflicted retail rather than wholesale.
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Old 11-30-2014, 07:31 AM   #8
Fred Brackin
 
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Default Re: Designing an Artillery piece - 3e vs 4e

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Originally Posted by BraselC5048 View Post

Also, one typical target would be an improvised barricade. Generally, it's a pile of crates, boxes and furniture, with a spare 1.5" titanium alloy starship hull plate (I did my homework and ran the engineering numbers) wedged in between them somewhere, or just propped up against the back side. That provides a heck of a lot of DR against bullets, perhaps DR 75, ?
DR 100 plus whatever the crates are worth.

The flipside of the diminished usefulness of area effects be they concussion or fragmentation is that future weapons can have very high direct penetration.

One of my favorite weapons from UT is the 25mm Shaped Charge warhead. Why? Because you so seldom _need_ to go larger. It does 5Dx3(10) and will easily inflict fatal wounds on armored targets through your improvised barricade.

Even the late model TL8 40mm HEDP launcher grenade from HT does 7D(10) and penetrates.

These weapons are also sufficiently convenient that every man in an armored squad can (and probably should) carry one.

So the improvised barricade is only built to defend against troops who do not possess serious armor piercing weapons and probably nobody lugs around a 105mm for combat inside starships.
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Old 11-30-2014, 10:10 AM   #9
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Default Re: Designing an Artillery piece - 3e vs 4e

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Originally Posted by Ulzgoroth View Post
5dx5 [5d+1] is right out of the cannon table on HT140. I don't know where you get a 25-pound shell, though. (The 105mm howitzer and 106mm recoilless rounds are listed at 40 and 38 pounds, respectively, but that would be for a complete shot so the shell alone is less.)
The M40 is listed as 6dx6(10) cr ex + 6dx4 cr ex. Though now that I look at it, it looks like the armor divisor on the cr ex attack is probably errata. If it's not, that (10) armor divisor will certainly help with blowing people in armor up.

He could be instead using the M2A1 stats, but that's not the gun he was specifically referencing - and the stats are still different from the ones he's been referencing.

The 25 pound weight comes from real M40 projectiles - the part that's spit out the end weighs about 10 kilograms on the heavier ones.

Quote:
As for rules for fragmentation...I don't believe there are any rules stated. However, there is an unstated but extremely consistent rule: fragmentation dice are 1d/20mm of warhead diameter. I have yet to find an exception in any weapon table.

It does seem pretty inadequate, but if you use rolled damage it has a somewhat decent chance of not being entirely useless...
Yeah, but that wouldn't get [5d-1] for a 105mm shell. No idea where that came from.

Also, there are ways to make a weapon have more or less or better fragments. I'm not sure why none are statted up in High Tech or Ultra-Tech (except HEC, which goes with the assumption of no fragments).
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Old 11-30-2014, 01:54 PM   #10
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Default Re: Designing an Artillery piece - 3e vs 4e

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Originally Posted by Langy View Post
The M40 is listed as 6dx6(10) cr ex + 6dx4 cr ex. Though now that I look at it, it looks like the armor divisor on the cr ex attack is probably errata. If it's not, that (10) armor divisor will certainly help with blowing people in armor up.

He could be instead using the M2A1 stats, but that's not the gun he was specifically referencing - and the stats are still different from the ones he's been referencing.
It's a HEAT round, the (10) is perfectly appropriate but only really good for killing somebody you're willing to give 106mm of personal attention.

The M2A1 pretty much perfectly fits "full size 105mm artillery shell", and the only difference from the cited stats is having [5d+1] instead of [5d-1]. Which could easily be a typo or misread.
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Yeah, but that wouldn't get [5d-1] for a 105mm shell. No idea where that came from.
Most likely mistake. I'm pointing out the rule because it is incompatible with getting 6 or 7 dice of fragmentation out of a shell without it being quite unpleasantly larger...

Though, actually, the 2-point difference might be very important to the matter at hand. 5d+1 averages 18.5 points and is quite capable of messing up people in DR 16, even if it's not dependably incapacitating. 5d-1 averages 16.5, which looks a lot less respectable.

...Of course, in a vacuum, having your armor penetrated by cutting fragments is going to give you considerable problems beyond the immediate injury. And if it's not a vacuum, the 5dx5 is pretty nasty.
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Also, there are ways to make a weapon have more or less or better fragments. I'm not sure why none are statted up in High Tech or Ultra-Tech (except HEC, which goes with the assumption of no fragments).
I have never seen any GURPS material addressing that in the slightest. Maybe because the Fragmentation rules are a low-resolution kludge with no moving parts...

(Aside from the ABF warheads and perhaps 'shrapnel' shells, which are modeled as RoF attacks.)
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