Designing an Artillery piece - 3e vs 4e

[BraselC5048]

Originally Posted by Langy

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.

I'm talking about a recoilless rifle firing full size 105mm howitzer rounds. The body armor isn't sealed. In the army, it's generally a ballistic cloth shirt (torso, upper part of the groin, arms, but not hands) and ballistic cloth pants (bottom part of the groin, legs, but not feet). Sometimes advanced body armor goes in there somewhere, usually on the torso, or more commonly trauma plates.

In the Navy, it's (from the inside:)

MCP vacc suit (everything but the head, absolutely no DR, no more than a pair of latex gloves, and head, DR 15 goldfish bowl helmet, only pressurized part).
Ballastic cloth shirt and pants as above, (DR 18, hostiles are usually DR 16 or less, it has more DR simply because it's a little heavier and thicker, and can stay at no encumbrance (sans any equipment) since the gravity on the ships lower then the others)
Uniform

The ballistic shirt and pants aren't connected at all, nowhere near enough to count as sealed. There won't be any DR against the 4d.

Originally Posted by Fred Brackin

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.

Actually, it's built to protect against troops with battle rifles firing APHC ammo. And it will. Our side's got a top secret (when it comes to the production process, nobody else has figured out how to make the explosive in industrial quantities) 11.5 mm round doing 5d+2 (10) damage, to get through body armor in a SMG round. Big advantage.

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.

APHC ammo in battle rifle and LMG's actually solves that issue. One interesting side effect is that although they're fine at inflicting casualties, although it might take two hits, they're bad at actually killing. Usually a hit to the head or vitals, or bleeding, are the few ways to die from small arms fire. They pi- just doesn't do enough damage post-armor.

Also, Dr 100 seems high for something that's structural shipbuilding grade, not armor grade. I used the stats for soft steel.

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...

Good idea. 6dx2 sounds about right.

Originally Posted by Langy

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.



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).

Actually, I was using the M2A1 stats from High Tech. It should be 5d+1, if I made a typo. For the 5dx8 [10d], I was using the 105mm Dp gun from the GURPS:WWII core rulebook. 7d fragmentation damage would be enough, although 6d would do in a pinch. 5dx5 concussion is plenty, although it might be worth it to reduce to 5dx4 to get better fragmentation.

Also, with the barricade, the idea was to simply blow it up. One hit will destroy it, if only by mangling the plate and destroying what's holding it up, the only question being what happens to the gunners right behind it. Likely casualties if they have any body parts above the barricade, likely casualties if ducked behind by being hit by a flying hull plate, if only broken bones.

The general idea of using it against a barricade was in the "initial clearing out the MG's in the cargo bay behind the blasted open 10-20 ft wide cargo door" phase, after which it wouldn't be as much use. The other use in with a landing party on a planet, same reason there's a trio of 81mm mortars on board. In that situation, often the vacuum issue goes away, and you can blow stuff up much better.

PS: Added more quotes in the middle of typing the post, sorry.

[fula farbrorn]

Originally Posted by Ulzgoroth

I have never seen any GURS 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.)

I have begun a pretty comprehensive work to give all the weapons in HT their proper damage and ROF for fragments, though i opted to make it piercing instead of cutting

and on the topic of making something that gives the fragmentation that we are talking about to damage this armour, its pretty hard if not impossible with the filler and metal hardness we are talking about, so i would just design it as needed and explain it away or use a MF load with some kind of AP dart, though i am not sure how feasible that would be

[Fred Brackin]

Originally Posted by BraselC5048

Also, Dr 100 seems high for something that's structural shipbuilding grade, not armor grade. I used the stats for soft steel.


Actually, I was using the M2A1 stats from High Tech. It should be 5d+1, if I made a typo. For the 5dx8 [10d], I was using the 105mm Dp gun from the GURPS:WWII core rulebook. .

<shrug> Use any stats you like but the general co9nsensus worked o0ut around here is that titanium delivers the same DR70/25mm that RHA does only at c. 5gms/cc instead of 8.

I wouldn't actually expect hull plates to be structural material either. The skeleton/framework carries the weight. The only reason to put plates that thick on is for micro-meteoroid protection.

The WWII corebook is 3e. Don't mix 3e and 4e explosive weapon stats. They are fundamentally incompatible due to basic rules changes. They might look similar in the range of 1 lb of TNT. That's 6Dx2 in both editions but in 3e 4 lbs of TNT is 6Dx8 and in 4e it's 6Dx4. In 3e damage goes up linearly. In 4e it goes up as the square root of lbs of TNT.

Then the rules about adjusting damage for distance are different too.

If you have to convert stats you need to change D of damage to lbs of TNT and then derive a new D using the 4e rules in Campaigns.

[BraselC5048]

Originally Posted by fula farbrorn

I have begun a pretty comprehensive work to give all the weapons in HT their proper damage and ROF for fragments, though i opted to make it piercing instead of cutting

and on the topic of making something that gives the fragmentation that we are talking about to damage this armour, its pretty hard if not impossible with the filler and metal hardness we are talking about, so i would just design it as needed and explain it away or use a MF load with some kind of AP dart, though i am not sure how feasible that would be

I'm not talking about a multi fletchette load. I'm talking about the shell splinters from a plain old HE 105mm artillery round. A round likely designed to give fewer, bigger fragments with more energy each - perhaps an internally grooved shell to control that. It would go "boom," and then fragments from the round, likely doing cutting damage, would be blasted away in every direction. 5dx5 [8d] would be great, but unlikely, 5dx5 [7d] would be plenty, and even [6d] would be serviceable, still always being a major wound. 5dx5 cr explosion is a reliable below 1/3rd HP fight ender at 2 yards (5 hex diameter), 5dx4 cr explosion is less so, often not going below 1/3rd HP reliably for ST 12 marines (although always a major wound).

In an atmosphere, a 5dx4 cr explosion has a definite full casualty radius of 2 yards, and an out-of-the-fight radius of 3 yards, and a 50-50 major wound radius of 4 yards, while a 5dx5 cr explosion adds one yard to all those. Going by GURPS:WWII - Dogfaces, at 5dx5 it would take 5 rounds to destroy a 50 x 20 ft wood frame house, 12 to knock down a brick house.At 5dx4 it would take 8 rounds to bring down a wood frame house, the same for a brick one.




Perhaps 5dx5 [7d] damage? With perhaps a -1 to hit with fragmentation? Or not?

Now going on a tangent...

I know that there's rules on being hit by fragments. I looked them up, and it's around a 7 or 8 or less to be hit at the edge of the danger area, which isn't actually all that bad, although it should be maybe 2 lower. I've actually used them, although adjusted for being from splinters from the starship's armor and hull in a narrow cone from a laser hit on the bridge. I think that's happened in three different battles I've played, although one of them had three different hits. And the poor SoB who got a starship laser to the chest, putting a hole right through it. I also once greatly reduced the chances of being hit and the falloff distance for one game where the characters were in a flying boat and the "shells" were only 20mm cannon shells.


As for an equivalent to beehive, it seems the best option is good old fashioned grapeshot. 50 round balls would be +6 to hit, and do an average of 32 pi++, and be doing 36 damage past DR 16 armor, easily killing a man, although it won't do anything other than 6 pts? of blunt trauma if the target is wearing trauma plates.

25 round balls would be +5 to hit, and be doing an average of 46 pi++ per ball, 22 damage past trauma plates, and an instant kill to the torso if not wearing them. enough to kill somebody past body armor with trauma plates.

No fancy armor divisors, and simple round lead balls, but with enough energy and size to kill past body armor anyway.

On the other hand, that assumes the muzzle energy of a full sized howitzer, which a recoilless rifle likely wouldn't have. Really, you're best off with an airburst of the regular high-frag HE round. The easiest way to do that would be to insert a simple time fuze in the nose instead of an impact fuze, with settings for 50 yards, 75 yards, 100 yards and the like, so no math is needed in action. Perhaps simply a scale around the edge of the fuze and turning something on the fuze, so you could simply interpolate intermediate settings. (They did the math using the gun's muzzle velocity when they designed the fuze.) Likely best to keep a few rounds with the time fuze already installed nearby, so you don't have to waste time installing them.



Back to the original question, it seems that a 5dx5 [7d] enhanced fragmentation (specifically designed for that) round would work well, if that can be done.

[fula farbrorn]

Originally Posted by BraselC5048

I'm not talking about a multi fletchette load. I'm talking about the shell splinters from a plain old HE 105mm artillery round. A round likely designed to give fewer, bigger fragments with more energy each - perhaps an internally grooved shell to control that. It would go "boom," and then fragments from the round, likely doing cutting damage, would be blasted away in every direction. 5dx5 [8d] would be great, but unlikely, 5dx5 [7d] would be plenty, and even [6d] would be serviceable, still always being a major wound. 5dx5 cr explosion is a reliable below 1/3rd HP fight ender at 2 yards (5 hex diameter), 5dx4 cr explosion is less so, often not going below 1/3rd HP reliably for ST 12 marines (although always a major wound).

In an atmosphere, a 5dx4 cr explosion has a definite full casualty radius of 2 yards, and an out-of-the-fight radius of 3 yards, and a 50-50 major wound radius of 4 yards, while a 5dx5 cr explosion adds one yard to all those. Going by GURPS:WWII - Dogfaces, at 5dx5 it would take 5 rounds to destroy a 50 x 20 ft wood frame house, 12 to knock down a brick house.At 5dx4 it would take 8 rounds to bring down a wood frame house, the same for a brick one.




Perhaps 5dx5 [7d] damage? With perhaps a -1 to hit with fragmentation? Or not?

Now going on a tangent...

I know that there's rules on being hit by fragments. I looked them up, and it's around a 7 or 8 or less to be hit at the edge of the danger area, which isn't actually all that bad, although it should be maybe 2 lower. I've actually used them, although adjusted for being from splinters from the starship's armor and hull in a narrow cone from a laser hit on the bridge. I think that's happened in three different battles I've played, although one of them had three different hits. And the poor SoB who got a starship laser to the chest, putting a hole right through it. I also once greatly reduced the chances of being hit and the falloff distance for one game where the characters were in a flying boat and the "shells" were only 20mm cannon shells.


As for an equivalent to beehive, it seems the best option is good old fashioned grapeshot. 50 round balls would be +6 to hit, and do an average of 32 pi++, and be doing 36 damage past DR 16 armor, easily killing a man, although it won't do anything other than 6 pts? of blunt trauma if the target is wearing trauma plates.

25 round balls would be +5 to hit, and be doing an average of 46 pi++ per ball, 22 damage past trauma plates, and an instant kill to the torso if not wearing them. enough to kill somebody past body armor with trauma plates.

No fancy armor divisors, and simple round lead balls, but with enough energy and size to kill past body armor anyway.

On the other hand, that assumes the muzzle energy of a full sized howitzer, which a recoilless rifle likely wouldn't have. Really, you're best off with an airburst of the regular high-frag HE round. The easiest way to do that would be to insert a simple time fuze in the nose instead of an impact fuze, with settings for 50 yards, 75 yards, 100 yards and the like, so no math is needed in action. Perhaps simply a scale around the edge of the fuze and turning something on the fuze, so you could simply interpolate intermediate settings. (They did the math using the gun's muzzle velocity when they designed the fuze.) Likely best to keep a few rounds with the time fuze already installed nearby, so you don't have to waste time installing them.



Back to the original question, it seems that a 5dx5 [7d] enhanced fragmentation (specifically designed for that) round would work well, if that can be done.

well a flechette load was just a suggestion, for fragments, as i said realistically larger fragments actually seem to produce on average smaller fragments with a few big ones throw in out of the driving bands or fuzes ETC
the inverse might hold true for a smaller bursting load

my advice is to just put it where you want without putting much more thought into it then that *or does that sound sacrilege to say here ?*

but something around 5DX5 and [6D+2] ? it means a fair amount of damage would still hit the target after the 16 DR and the cutting modifier

[BraselC5048]

Originally Posted by fula farbrorn

my advice is to just put it where you want without putting much more thought into it then that *or does that sound sacrilege to say here ?*

but something around 5DX5 and [6D+2] ? it means a fair amount of damage would still hit the target after the 16 DR and the cutting modifier

Good idea, and it certainly would.

[Langy]

The ballistic shirt and pants aren't connected at all, nowhere near enough to count as sealed. There won't be any DR against the 4d.

That shouldn't matter. The 4d damage wouldn't ignore non-sealed armor.

[BraselC5048]

Originally Posted by Fred Brackin

The WWII corebook is 3e. Don't mix 3e and 4e explosive weapon stats. They are fundamentally incompatible due to basic rules changes. They might look similar in the range of 1 lb of TNT. That's 6Dx2 in both editions but in 3e 4 lbs of TNT is 6Dx8 and in 4e it's 6Dx4. In 3e damage goes up linearly. In 4e it goes up as the square root of lbs of TNT.

Then the rules about adjusting damage for distance are different too.

If you have to convert stats you need to change D of damage to lbs of TNT and then derive a new D using the 4e rules in Campaigns.

Thanks for the idea. It'll be useful.

Originally Posted by Fred Brackin

<shrug> Use any stats you like but the general co9nsensus worked o0ut around here is that titanium delivers the same DR70/25mm that RHA does only at c. 5gms/cc instead of 8.

I wouldn't actually expect hull plates to be structural material either. The skeleton/framework carries the weight. The only reason to put plates that thick on is for micro-meteoroid protection.

The plates are for pressure bulkheads. 5 ft by 5 ft square, between the main frames and the intermediate pressure frames. Using smaller frames every 5 feet between the main structural frames actually wound up saving weight versus a bigger, thicker plate. The 1.5" thickness is to hold against a 1.5 atmosphere pressure differential while stresses remain at or below the fatigue limit, so the hull will pretty much last forever without having to worry about metal fatigue. Keeping design stresses below the fatigue limit also provides a built-in margin of safety, so failure point is a little over 3 atmospheres pressure differential. Like I said, I did my engineering homework and ran the numbers, and that's what came out.

The intermediate pressure frames are (going from memory here, I didn't go and dig out the sheet of paper with actual numbers) something like a 6x8 inch box beams, with walls something like an inch think. Or it might have been 4x6 inches instead, with walls around an inch thick. The density of the ship as a whole is about 2/3rds of a metric ton per cubic meter. The ships I did the math for uses much of that weight for armor, merchants use that weight for cargo, and their holds still often wind up with a lot of empty space when carrying a cargo of metal billets. (Reached maximum mass limit for cargo.)

It's a Traveller style starship, sort of, although without actually using any of GURPS Traveller, and at TL 8+a bit of^. The exact design and weapons doesn't match anything you'd recognize, since my setting and it's technology is just so different.

Originally Posted by Langy

That shouldn't matter. The 4d damage wouldn't ignore non-sealed armor.

Certainly agree there. A blast is a blast, regardless of whether your armor's sealed or not, it's all blunt trauma and limb ripping anyway. On the same note, why the heck does armor help at all against falls? A suit of plate is just more inertia and a bigger splat when you hit the ground.

[Langy]

Originally Posted by BraselC5048

Certainly agree there. A blast is a blast, regardless of whether your armor's sealed or not, it's all blunt trauma and limb ripping anyway. On the same note, why the heck does armor help at all against falls? A suit of plate is just more inertia and a bigger splat when you hit the ground.

Then I'm not sure why you said there'd be no DR protecting against the explosion, and did so in a way to imply that that was because the armor isn't sealed.

[fula farbrorn]

Originally Posted by BraselC5048

Certainly agree there. A blast is a blast, regardless of whether your armor's sealed or not, it's all blunt trauma and limb ripping anyway. On the same note, why the heck does armor help at all against falls? A suit of plate is just more inertia and a bigger splat when you hit the ground.

that is actually something i have been thinking about, how come GURPS doesnt let blast damage do more localized damage, while a small blast like a handgrenade might not rip off limbs or such, larger blasts do carry with them a host of damage, for example occular or concussions