Low Tech cannons mortars and shells

[Polydamas]

Originally Posted by Varyon

At low TL's, I don't think fragmentation is properly understood, so it might have a maximum of 1/2 the explosive damage, and I'd probably treat shells that aren't designed with any specific amount of fragmentation in mind as having 10% to 20% of the explosive damage in fragmentation

My understanding is that it was only after WW II that engineers go through every exploding munition and systematically design it to kill and maim as many people with fragments as possible, Eg. the old 'pineapple' grenades were designed to be easy to grip with a wet or muddy hand, any benefit to fragmentation was accidental. Its just so much harder to make anything other than a simple casing, and gunners are really really concerned that you get "does not explode in the tube" right.

[Anthony]

Originally Posted by Rupert

However, the way GURPS does fragments implies that as the warhead gets bigger the energy put into the fragments drops, as a fraction of the total (which is questionable), and for artillery shells it could well be negligible.

That has more to do with the rules for blast damage being broken than with the rules for fragments being broken. Fragment damage being linear in shell diameter is entirely reasonable, the problem is that radius for blast effects should also be near linear in shell diameter, not 3/2 power (what it actually should be in both cases is damage that's linear, and also a wounding multiplier that's linear; a bomb that's 8x more massive produces a given overpressure at 2x the range but also for 2x the duration, and it produces fragments with 2x the penetration but also 2x the wound channel).

[Rupert]

Originally Posted by Fred Brackin

With a fragmentation jacket of constant thickness (resulting in fragments of unchanged size), fragmentation will go up as the square while explosive charge will go up as the cube.

Even if fragmentation jackets got thicker the interface between the jacket and the charge only goes up as the square.

Ah, but the mass of the thicker jacket goes up as the cube (and bigger shells do have thicker walls, assuming similar velocities), so unless there's too little bursting charge to give a similar velocity to the fragments they'll eat up energy proportional to the cube of calibre. This also will either means the fragments' damage should go up faster than linearly with calibre, or that larger shells should also have more of them - I've posted on this before.

In the real world, shells might have more fragments with increasing size or bigger ones, depending on what the designer wanted (and on their TL4 and thus ability to adjust such things). For anti-material work (shooting up ships, counter-battery fires, etc.) you want big fragments, while for anti-personnel work you want lots of fragments to get complete coverage and they don't have to be very energetic.

[Rupert]

Originally Posted by Polydamas

My understanding is that it was only after WW II that engineers go through every exploding munition and systematically design it to kill and maim as many people with fragments as possible, Eg. the old 'pineapple' grenades were designed to be easy to grip with a wet or muddy hand, any benefit to fragmentation was accidental. Its just so much harder to make anything other than a simple casing, and gunners are really really concerned that you get "does not explode in the tube" right.

People have been trying to make better shells, in this and every other respect, for centuries.

For example, shrapnel shells were a (successful) attempt to get round the problem of poor shell performance by effectively making a grapeshot round that didn't start spreading until it was well downrange. The weight of the balls in the shrapnel shells was carefully calculated so each one would have just enough energy at maximum effective range to cause a casualty, so as many balls as possible could be used, and this calculation included allowance for the velocity of the shell and the boost the burster charge gave. Later versions fired the balls out of the shell like a shotgun, rather than wasting energy breaking up the shell casing, giving better and more consistent results.

Another example would be the changes in shell material from iron to steel, and then variations in the steel alloy to improve fragmentation performance (and also to improve cost, allow higher gun pressures, and so on, of course).

While TL7 saw many advances in shell design and construction, there was plenty going on in TL5 and TL6 as well. Finding out what the optimal amount of burster was for various roles, for example. The development of the very high capacity shells for aircraft cannon (GURPS would call them SAPHEC) by the Germans in WWII for another (though you could make a case for these being a TL7 invention).

[Ulzgoroth]

Originally Posted by Polydamas

My understanding is that it was only after WW II that engineers go through every exploding munition and systematically design it to kill and maim as many people with fragments as possible, Eg. the old 'pineapple' grenades were designed to be easy to grip with a wet or muddy hand, any benefit to fragmentation was accidental. Its just so much harder to make anything other than a simple casing, and gunners are really really concerned that you get "does not explode in the tube" right.

If you mean 'carefully tweak the material properties and fine structure of fragmenting casings', you're likely right, but the 18th century shrapnel shell is right there.

[Varyon]

Originally Posted by Rupert

Fragmentation damage is 1d per 20mm of warhead diameter if there's enough fragmentation to give a fragmentation effect as GURPS understands it.

I've seen this figure mentioned before, but can never remember it when these threads pop up. Is it actually stated somewhere in the GURPS books, or is it just something that has been extrapolated from existing weapons? Also, what impact should various means of increasing fragmentation (shell walls specifically designed to fragment, having premade fragments inside of the shell, etc) have on this?

Originally Posted by Polydamas

My understanding is that it was only after WW II that engineers go through every exploding munition and systematically design it to kill and maim as many people with fragments as possible, Eg. the old 'pineapple' grenades were designed to be easy to grip with a wet or muddy hand, any benefit to fragmentation was accidental. Its just so much harder to make anything other than a simple casing, and gunners are really really concerned that you get "does not explode in the tube" right.

I think there were low tech attempts to increase fragmentation by including nails or other preformed fragments inside of the grenades, like the Chinese land mine on LT86 (that used lead balls... which somehow do crushing damage instead of the piercing damage of most high-velocity lead balls in GURPS).

Originally Posted by Anthony

That has more to do with the rules for blast damage being broken than with the rules for fragments being broken. Fragment damage being linear in shell diameter is entirely reasonable, the problem is that radius for blast effects should also be near linear in shell diameter, not 3/2 power (what it actually should be in both cases is damage that's linear, and also a wounding multiplier that's linear; a bomb that's 8x more massive produces a given overpressure at 2x the range but also for 2x the duration, and it produces fragments with 2x the penetration but also 2x the wound channel).

So, you're saying that it would be more appropriate for explosions to scale with the cube root of explosive weight (rather than the square root they currently use)? The wounding multiplier would be a bit of a pain to try to work through; it might be better to just have damage scale as the 2/3 power of weight. If already redoing things, it would probably be a good idea to adjust fragmentation so that the skill isn't always 15, but is rather dependent on how much fragmentation the explosive produces (more fragments means higher skill)... and maybe make them pi instead of cut, probably with a poor armor divisor (ideally, the armor divisor would go down with fragmentation damage, to represent larger fragments having more difficulty getting through DR but causing more severe wounds when they do - the latter is already handled by using 2/3 power - but that might be a bit too difficult to implement in practice). Maybe have an option when the explosives are designed to have a tradeoff between fragmentation damage and skill (more fragments means higher skill, but as they are smaller they each deal less damage).

[Anthony]

Originally Posted by Varyon

So, you're saying that it would be more appropriate for explosions to scale with the cube root of explosive weight (rather than the square root they currently use)?

Something of that type. It's somewhat more complicated, but the standard rule of explosive scaling is that you can start with a reference explosion, and then for any other size of explosive you can determine overpressure at any given distance by finding the overpressure from the reference explosion at a distance of (actual distance) / (cube root of ratio of actual explosive weight to reference explosive weight).

[Rupert]

Originally Posted by Varyon

I've seen this figure mentioned before, but can never remember it when these threads pop up. Is it actually stated somewhere in the GURPS books, or is it just something that has been extrapolated from existing weapons? Also, what impact should various means of increasing fragmentation (shell walls specifically designed to fragment, having premade fragments inside of the shell, etc) have on this?

I don't recall if any author actually stated it. However, all of HT's and UT's warheads, shells, etc. follow this rule, allowing for rounding, except some of HT's hand grenades.

Well, following the rapid fire table, doubling the number of fragments should give +1 to hit, and would reduce each fragment's damage to 70% of the original. Four times as many would be +2 to hit and x0.5 times the damage. Basically the same as adjusting the number of pellets in a shotgun shell, just don't worry about the exact numbers, just the ratios.

In my view every doubling of shell diameter should also probably give a +1 to hit, probably using 40mm as a baseline so 40mm+ gets +0, 80mm+ a +1, and so on. Going down I'd be generous and say 20mm and under gets -1 and 10mm and under gets a -2.

I think there were low tech attempts to increase fragmentation by including nails or other preformed fragments inside of the grenades, like the Chinese land mine on LT86 (that used lead balls... which somehow do crushing damage instead of the piercing damage of most high-velocity lead balls in GURPS).

Maybe they're considered to be fairly slow, like sling bullets? Otherwise, I have no idea. The 14d explosion is going to be far more of a worry for most characters anyway - the 'fragments' are really just icing.

...and maybe make them pi instead of cut, probably with a poor armor divisor (ideally, the armor divisor would go down with fragmentation damage, to represent larger fragments having more difficulty getting through DR but causing more severe wounds when they do - the latter is already handled by using 2/3 power - but that might be a bit too difficult to implement in practice).

Cutting actually describes fragments pretty well - compared to injury they penetrate poorly (though perhaps not as poorly as they should), and they tend to be irregular and jagged shapes that cut and tear.

[Polydamas]

I'm sure there were attempts to load a bomb with nails, potsherds, scrap iron, pistol shot, etc. in the 15th-17th century, I don't think these things were scientifically tested in the manner of Cold War and later military engineering.

Originally Posted by Ulzgoroth

If you mean 'carefully tweak the material properties and fine structure of fragmenting casings', you're likely right, but the 18th century shrapnel shell is right there.

The original shrapnel shell did not use fragments at all, it was meant to work as an airbust which scattered balls like a Cold War claymore mine.

[Varyon]

Originally Posted by Rupert

Well, following the rapid fire table, doubling the number of fragments should give +1 to hit, and would reduce each fragment's damage to 70% of the original. Four times as many would be +2 to hit and x0.5 times the damage. Basically the same as adjusting the number of pellets in a shotgun shell, just don't worry about the exact numbers, just the ratios.

That matches my thoughts, yeah.

Originally Posted by Rupert

In my view every doubling of shell diameter should also probably give a +1 to hit, probably using 40mm as a baseline so 40mm+ gets +0, 80mm+ a +1, and so on. Going down I'd be generous and say 20mm and under gets -1 and 10mm and under gets a -2.

So, 5mm (if possible) is [1] at Skill 12, 10mm is [1d-2] at 13, 20mm is [1d] at 14, 40mm is [2d] at 15, 80mm is [4d] at 16, and so forth. And perhaps grenades can be specifically designed to adjust these, with every -1 SSR to damage giving +1 to skill and every +1 SSR to damage giving -1 to skill.

Originally Posted by Rupert

Maybe they're considered to be fairly slow, like sling bullets?

Lead sling bullets do pi, not cr - although now that I check LT, I notice that Harsh Realism for Ranged Weapons does indeed suggest downgrading to cr. So maybe that particular Harsh Realism effect is automatically in play for the landmine?

Originally Posted by Rupert

Cutting actually describes fragments pretty well - compared to injury they penetrate poorly (though perhaps not as poorly as they should), and they tend to be irregular and jagged shapes that cut and tear.

While it's true that they are jagged and cut and tear rather than crush their way through soft tissue like a bullet, they are also typically rather small and, by my understanding, tend to wound and kill by penetrating into flesh and disrupting organs (and causing bleeding) rather than slicing bits off. That feels more like piercing to me; in terms of resisting penetration it probably has more in common with cutting, true, but GURPS typically lumps cut and pi together anyway when split DR is in play. I don't think fragments should be as dangerous to the undead (or machines, or homogenous targets) as they are to the living, and treating them as piercing - so that IT:Unliving and IT:Homogenous results in reduced wounding - handles that nicely. Although maybe I'm mistaken, here?