Re: Low Tech cannons mortars and shells
 

It may well be that 3d6 is the wrong distribution to represent the scattering of fragments through a sphere or a cone, but I would start by getting some numbers or back-of-the-envelope calculations, see how they really work, then see how well or poorly different mechanics model them.

A detailed rule might say that anyone within oh 75 yards of detonation (and within the cone of that applies) is attacked with skill A, anyone up to 150 yards is attacked with skill B, and so on. That is the most complicated rule I can imagine actually using, but its not all that complicated.

Re: Low Tech cannons mortars and shells
 

In reality, if you're inside a certain distance (dependant on the shell) and inside the fragmentation pattern you will get hit, and if you're outside that the chance drops off fairly rapidly. A well-designed modern (anti-personnel) shell also has fragments that lose energy very quickly past that saturation point, so damage drops off as well as hit chance.

However, I don't think that'd result is a whole lot of fun, given the extremely binary results this tends to bring, so using the RAW or modifications of them is probably a better way to go.

For low TL shells I'd consider changing the base hit chance to 7+TL from the standard 15-. At TL4 possibly increase the per-fragment damage by 50% or 100% to reflect their large size (at TL3 the shells tended to break too quickly, so the explosion didn't impart much energy to the fragments). Possibly also increase the 'Rcl' from 3 to 4 (fewer fragments also means less chance of multiple hits).

For modern TL8+ shells that are designed for anti-personnel work, reducing damage to buy more hits is reasonable - every halving of energy means twice as many fragments, and thus +1 to Hit but doing 70% of the base damage. Shells with very dense fragment patterns should also have reduced maximum radius (they're so small they lose energy very fast), but might have Rcl 2.

I'd definitely adjust the base hit number based on shell/bomb size (as I mentioned earlier in the thread).

If you want to get picky, a 1/2D radius would be reasonable, but I'm not sure what it would be (probably the fragment damage dice times some constant, and that constant would be different for pre-formed 'fragments' like balls).

Re: Low Tech cannons mortars and shells
 

You should probably also look at base damage and type. 2D Cutting for grenade frag is a lot. 2D Cutting is a full-sized axe in the hands of a strong man. Grenade frag isn't that big and doesn't hit that hard. Ball bearing like "frag" as in the Diehl and claymores could be 2 or 3D Piercing easily enough.

Even frag from larger shells that is larger than grenade types may be approaching the axe's cutting edge in size (and of course coming in at a higher velocity) but it doesn't have anything like the same momentum.

I'd do away with cutting frag and make it all Piercing quite possibly with some of the types having an Armor multiplier to represent their poor sectional density.

Of curse, the very small fragments from grenades make up for their low individual damage by producing a _lot_ of hits;

The Mythbusters were testing "Diving for cover" against grenades and first detonated frag grenades (a MK2 "pineapple" and an M67 "baseball") at 5 yards against a man-shaped outline on a large piece of standard plywood. Both grenades produced c. 200 hits at 5 yards (the M67 made a neater and less "clumpy" pattern) but no daylight was seen through the 1/4 inch plywood.

That's not 2D6 per fragment and no manipulation of the Rapid Fire system will give you enough hits. I'd say abandon the Rapid Fire rules for this application. This is just too different from spraying bullets from an assault rifle or smg.

Re: Low Tech cannons mortars and shells
 

Rupert, that makes me think of a D&D-type mechanic for Cold War and later artillery where an explosion has a fragmentation radius, anyone within it is hit once, and anyone out to say three times the radius is hit by chance. (In D&D, maybe they get a Reflex or DX save).

If you assume that a standing soldier has an area of about 1 square yard or meter, then I think you could roughly estimate the chance of being hit at a given range by the ratio of the number of projectiles to the area of the end of the cone or the surface of a sphere at that range.

Re: Low Tech cannons mortars and shells
 

An alternative method is simply to assume an automatic hit so long as the target is within the fragmentation radius, and that this hit is actually in the form of impacts all over the body. You roll a random hit location once to see where the most significant hit is (or hits are, it could represent several larger fragments or whatever), and roll damage for that hit to represent the damage to that body part. The wounds elsewhere are insignificant compared to that big one, so need not be accounted for. Potentially, you can further assume anyone who isn't fully covered with armor takes some minimum amount of damage (probably something like 1 point per 1d fragmentation) to represent the fact that any uncovered part of the body gets damaged a bit by small fragments, in case the notable fragment fails to penetrate the DR of that particular hit location (if this minimum damage is enough to cripple, you may want to assess that as well; if the character is fully but not uniformly armored, subtract the lowest DR from the minimum to determine how much penetrates).

Or maybe roll as per the default rules (ideally modified as discussed above, with certain explosives having higher effective skill), but in the case of no penetrating hit (due either to the fragmentation roll resulting in a miss or any hits from it failing to get past DR) you still assess the above minimum damage.

EDIT: I'd probably be inclined to only have the Vitals, Eyes, Skull, Arteries/Veins, Joints, and possibly Extremities (Hands and Feet) be struck by random chance, and not include them in the minimum damage result. That assumes the explosion is in front of a standing character (or above a supine one); different orientations might change this (notably, Skull would become valid and Face would become invalid for an explosion above or behind the character, while Neck would probably become invalid for an explosion above the character, as the Skull - and helmet - would give it some protection). Very small targets might similarly not have to worry about that minimum damage result - although I'd be inclined to have a miss by 1 mean they still suffer that minimum damage, just like a human who is missed, and maybe a miss by 2 means they suffer that minimum damage to only a single random hit location.

Re: Low Tech cannons mortars and shells
 

At that point I'd just port the rules from something like GDW's Twilight:2000, or make a hack from them. The thing is, while we can make estimates for things like Shrapnel shells, grenades and HE shells are harder to do - they don't always have consistent fragment numbers, and we don't always know what those numbers are either.

However, military literature does often state 'kill' and 'casualty' zones (with differing definitions depending on the time and place of writing, just to make life 'interesting') from which we can extrapolate numbers, if it seems worth the bother (and these days I don't think it is, for me).

Re: Low Tech cannons mortars and shells
 

I'm fine with the rules for the things you list, the results are adequate and I don't need more accuracy. The problem that I was addressing was, AFAICT, rules for the area of effect for multiple projectile cannon rounds like canister, shrapnel and beehive simply do not exist.

Re: Low Tech cannons mortars and shells
 

There's one case where there's a special rule for an attack like this given that I'm aware of - the Claymore mine description, HT189.

Re: Low Tech cannons mortars and shells
 

They do, although they're a bit cryptic. See "Multiple Projectiles" in High-Tech, pp. 172-174, and the example weapon descriptions in the same book.

It seems best to start with the M18A1 Claymore, HT p. 189, which has a clear description of the effects. Most of the weapons under "Cannon", pp. HT 138-141 list damage for canister, shrapnel or beehive, depending on what they used.

Re: Low Tech cannons mortars and shells
 

I don't see rules on High Tech pages 172-174 for hitting multiple targets with multiple-projectile ammunition. Could you explain where you see them?

The rules for a Claymore mine specify the shape of the area effected and spell out rules similar to the Fragmentation rules.