Slings, realistic physics, The Deadly Spring
 

Has anyone had any luck modelling slings in a slightly more plausible manner than the current one?

Can one plug them into Douglas Cole's The Deadly Spring in any way?

Re: Slings, realistic physics, The Deadly Spring
 

We could probably come up with some rough estimates if we had any empirical data at all on slings. What we really need to know is the efficiency with which the energy is transferred to the bullet and also the amount of time that the energy is being applied to the bullet.

It's not as easy to do this with the sling, though, as it is with the bow. With the sling you don't have uniform acceleration. It's completely different from a bow. It's more like swinging a baseball bat.

I found this after a Google search. I don't understand most of it, though.

He's talking about propelling a 100g stone to 32m/s.

That's only about fifty Joules.

If you care to guess this guy's ST score, I can try to apply my melee damage house rules to get you a rule you can use. All I'd be doing is figuring his arm's wattage for his Basic Lift and then applying an efficiency modifier to get the final energy, but that should work okay enough for what we're doing. I just need to know that particular example's Basic Lift to get the efficiency of his examples that we can then form into a generalized rule.

Re: Slings, realistic physics, The Deadly Spring
 

I've got a decent study where the author compares previous experiments and performs some of his own. It's called Expertimentation in Sling Weaponry by Eric T. Skov and is available online. It's an Anthropolgy MA thesis from the University of Nebraska, this year.

Unfortunately, only fairly light projectiles are used, but even so, it's light-years ahead of the other literature I've read.

Re: Slings, realistic physics, The Deadly Spring
 

Hmmmm, from what (little) I know about slings is that they seem to act mostly like a pendulum arm, increasing the torque of your throw, with a bit of a spring like action going on at the end so I would think that you'd need to do some heavy retooling of Mr. Cole's Deadly Spring engine to make one work.

Re: Slings, realistic physics, The Deadly Spring
 

There is some published work on modelling of one-armed catapults (both onager-style, with springs made of wound tendons, and trebuchet-style, with big damned weights) that looks at the gain in efficiency from having the missile in a sling at the end of the arm, rather than in a rigidly fixed cup. That's effectively equivalent to a human arm holding a conventional sling. I would recommend looking at the mathematical modeling for that case, at least as an intuition aid.

Bill Stoddard

Re: Slings, realistic physics, The Deadly Spring
 

To begin with, I was thinking I'd input some real world experimental results into his firearms model, to check what our performance benchmarks ought to be.

At least it would guide me toward quick and dirty fixes to slings, before they become relevant in my campaigns.

Re: Slings, realistic physics, The Deadly Spring
 

The problem with a sling is that it's a messy biomechanics problem; muscle isn't as simple to model as springy materials.

For a very simple throwing arm, the total energy is (torque) * (angle between minimum and maximum), and the efficiency is (moment of inertia of the projectile) / (moment of inertia of projectile and arm). Unfortunately, the amount of torque an arm can apply is time-dependent. Using a constant-power approximation instead of a constant-force approximation, energy scales as P^2/3 * I^1/3. A sling increases the moment of inertia of the projectile without a corresponding increase in arm inertia or projectile weight; the combination of increased total inertia, increased efficiency, and no increase in projectile mass results in a faster, higher energy projectile.

Note that this is basically the same as the physics of swinging weapons, and the virtue of tip-weighted weapons is that they have a greater moment of inertia for the same weight.

Re: Slings, realistic physics, The Deadly Spring
 

I looked around a bit, and Chris Harrison presented some numbers that suggested sling bullets could hit as fast as 90 m/s.

That's a lot more than the 38 m/s provided by a staff sling in Richardson's website. I will admit I find 90 m/s somewhat optimistic, but some of the ranges claimed by slingers (and the actual Guiness Book world record of over 437m with a 52g projectile from a 51" sling) suggest an impressive ability. Using a simple trajectory calculator, this could be achieved at a 45-degree release angle at just above 65m/s (no air resistance), or as little as a 16 degree angle at 90 m/s.

Let's assume a 50g projectile at 75 m/s, then.

That's about 140J and an effective diameter on the order of 18.5mm.

Penetration by the firearms model would be 1d (3.5pts) and the wound modifier would be north of 3.6, so if we call it 1d pi++ that probably understates the impact a bit.

I'd suggest an armor multiplier vs rigid armor, though.

For the 30-40m/s and 28g that Thom Richardson usually throws down, you'd be in the neighborhood of 1.2 points on the average; call it 1d-2 pi++

So if the higher-end limits are to be believed, against an unarmored man, you would look at an average of about 3.5*3.5 = 12 points, with an upper end on the order of 21 points, enough to reduce an average man to -HP in one shot at the extreme, and KO him on the average with a "torso" hit. That breaks the RAW max of pi++ for GURPS, though. more rationally, you'd only approach the upper end on a vitals hit.

I was thinking 90m/s was pretty darn optimistic, and certainly "world record" is upper end. But it does suggest that imparting such energy is feasible (and a strong bow is on that order as well).

Re: Slings, realistic physics, The Deadly Spring
 

To take a simple benchmark to start with, fairly typical lead glandes are ovoid or biconical in shape, measuring 29mm x 18mm x 13mm and weigh just over one ounce or 35-40g. Call it an ounce precisely, or 28g, if that makes it simpler, as that is very close to a median weight of discovered examples.

Experiments suggests that they attain a speed of 45m/s, even with inexpert users, assuming they are willing to practise for a few weeks. If not, speeds of 30m/s are more common.

It seems that anyone with the skill at DX+2 in GURPs terms, which is fairly likely for professional military slingers, would attain at least 45m/s and likely more.

Range is at least 100m and up to 300m, depending on methods. The longest cast, not yet verified by the Guiness Book of World Records, is 505m, using just such a 40g ovoid lead glans.

Striking with the pointed end, what kind of damage ought that be doing?

Edit: The impact cross-section of such a biconical projectile is 0.79 cm2.

Re: Slings, realistic physics, The Deadly Spring
 

Oh yeah, that would give you good bench marks to work off of but the hard part would be you would have to come up with a whole new way to translate ST into damage or more correctly into velocity (we can fub things a bit here and just count final velocity at the point of launch and use Dice rolls to simulate throws with more or less oomph).

As a base I'd say that arm velocity could equal ~8m/s*SQRT(ST/(2.6*cube root(body weight + weight of stone in KG))) then times that by how much of a boost the sling gives you. As for how much of a boost it gives you, well as a start we can fudge around with how much of a lever the sling acts like and compare it to known results. One way to bench mark this is to get throw a couple rocks with your hand and measure the velocity at release and then use a sling and do the same.

Re: Slings, realistic physics, The Deadly Spring
 

If you say someone is able to generate Watts equal to three times their Basic Lift per arm at the maximum, and that a sling has an efficiency of around ninety percent (which is just me making something up), and that attacking with a sling takes between a third of a second and three-quarters of a second (depending on swing style), then what you end up with is:

A minimum of Joules equal to nine-tenths of Basic Lift.

And a maximum of Joules equal to nine-tenths of two-and-a-quarter times Basic Lift.

So that seems to fit the data fairly well. I'd probably call the weaker attack a regular attack and the stronger attack an AoA (Strong) and leave it at that. And I'd probably come up with some Strongsling perk that mimics Strongbow, if you're using that one in your game.

Re: Slings, realistic physics, The Deadly Spring
 

As usual, experimentation reveals that typical projectile weights in historical military use weren't the most effective designs, but instead some compromise between economy, logistical concerns and sufficient effectiveness.

2-3 oz. glandes outperform 1 oz. ones in more or less every way that you can mention. They even attain more initial velocity.

But they were less common because the improved performance was less important than having more ammunition for the same amount of lead.

Since adventurers often worry more about the effectiveness of each shot than economy and logistics, I'd think that looking at 100g, 200g and even 450g designs would be worthwhile.

As a GURPS rule of thumb, standardised shot are at least +1 Acc commpared to even carefully chosen stones. Found stones are -1 to hit compared to that.

I see no evidence that the staff sling rates a +1 Acc compared to any other design, especially since it is very awkward for point targets in straight flight paths. It does get longer range, though, with the same projectiles. Also, it allows for heavier projectiles without loss of velocity, which will improve both range and damage, but increase ammunition Cost and Weight.

Lead ovoid/biconical glandes outrange stones of the same weight by around 50%, fairly consistently.

Re: Slings, realistic physics, The Deadly Spring
 

This site might help out a bit:
http://slinging.org/index.php?page=t...eorge-alsatian

It goes into three models covering how a sling effects acceleration.

Re: Slings, realistic physics, The Deadly Spring
 

I have a few simple houserules, but not on the deadly spring level:
http://forums.sjgames.com/showthread.php?t=74207

Re: Slings, realistic physics, The Deadly Spring
 

I'm leaning toward using cr damage to model slings, but using an AD to model the abysmal performance against any kind of armour. This would range from (0.5) to (0.1), for what we usually think of as sling ammunition, but AD(1) is entirely plausible for 1-lb stones, as those have a wounding mechanism that is qualitatively different from that of bullets.

Re: Slings, realistic physics, The Deadly Spring
 

Re: Slings, realistic physics, The Deadly Spring
 

Well if your going that route then T.Bone's GLAIVE could work as a nice middle ground, it's meant for 3rd ed but it has some nice rules on how weapon length increases swing damage.

http://www.gamesdiner.com/glaive

In his mod
Swung weapons have a Swing Effect Modifier equal to (Effective weapons length (max equal to your arm length)+arm length)*1.5)/how many hexes tall your are in feet

And swing damage adds = SQRT(weapon weight in lbs*Swing effect mod*2)

So assuming a ST10 Joe Normal with a ~3ft arm, a 2ft sling and a 3oz stone you'd get swing effect ((3+2ft)*1.5)/3 = 2.5 and a damage adds of SQRT(0.1875*2.5*2) which comes out to 0.97 which we'll round up to +1 giving him a swing damage of 1D+1 for sling.

After that we'd just need to figure out range.

Re: Slings, realistic physics, The Deadly Spring
 

I've already posted the results of Thom Richardson's Egyptian sling the last time this subject came up.

Re: Slings, realistic physics, The Deadly Spring
 

Sorry for being the one to ruin your party, but wouldn't this ruin the way sling damage (both penetration and wounding) compares to thrown weapons, woomeras, and swung/thrusting mêlée weapons?

Re: Slings, realistic physics, The Deadly Spring
 

Pretty much all ST-based weapons have questionable damage physics; bows just happen to be the easiest to analyze because the biomechanics don't matter, you can get the same results from a mechanical crank pulling the string.

Re: Slings, realistic physics, The Deadly Spring
 

I imagine that when you get down to the details even "universal" human features like how the joints articulate and where muscles attach might vary and screw with the end results.
My arm bones are exceptionally thick and don't allow full or hyper-extension. So I can never get good at holding bows pulled back.

Re: Slings, realistic physics, The Deadly Spring
 

Sure.

But it makes more sense to class slings with bows and crossbows in performance than it does to class them with short-ranged thrown weapons. It doesn't mess too badly with anyone's suspension of disbelief to have thrown weapons massively outpenetrate longer ranged missile weapons, as that result was also expected in reality.

Granted, GURPS overstates the difference at high ST levels, but I think I can live with that for the time being. .357 Magnum slings, however, are disconcerting.

Re: Slings, realistic physics, The Deadly Spring
 

Indeed.

Of course, there are other researchers achieving velocities of at least 50% and sometimes 60% higher than he is, even with the same sling and same ammunition. Those are not even master slingers, but simply young people in decent condition who train for several weeks. See Eric T. Skov, Experimentation in Sling Weaponry.

Richardson himself admits that his ranges are below what most other tests yield and acknowledges that he might be using inferior technique.

So I'd be inclined to believe that his results are not representative of the sling as a weapon of war, even if the sling he used may have been used in warfare. It is, of course, far safer and more comfortable for a novice to avoid full-power launches in favour of more leisurely throws.

This also matches results that people from cultures that use the sling as a toy and shepherding tool achieve. If they are not specificallly instructed otherwise, they'll use a sling, ammunition and technique which are optimised for accuracy at short ranges and which do not reach very far. That's good for scaring wolves, killing small game and anything else these cultures would actually use the sling for.

However, just like most warbows are not designed or used in the same way as toy bows or even bows for hunting small game, this does not tell us much about the use of war slings. I'd expect them to at least match the velocity achieved by Skov and probably exceed it. Indeed, the ranges confirmed by the small fraternity of enthusiastic slingers indicate that much higher velocities must be achievable with training. If you can launch a 40-50g stone more than 450m, an equally skilled user with a lead glans can achieve significantly more impressive velocities and ranges than Richardson. There's no way to come close to that range with an initial velocity around 30m/s, not unless you suspend gravity and air resistance.

Unfortunately, no one among the very small fraternity of skilled slingers has as yet performed sufficiently exhaustive testing with slings designed to kill humans at long ranges, probably because that's not a competative sport. Some of the best slingers for achieving long casts are competing in an event where only stones may be used, for example. They'd need to get used to a new type of sling and a new shape of projectile to demonstrate the range and velocities achivable with replicas of the archeological lead glandes. Not to mention that lead glandes, unlike stones, are not easily visible in flight.

As a result, we lack reliable velocity data for people who actually can sling with anything approaching the power to be useful on a battlefield. Extrapolating from the distance of world records, does, however, indicate that velocities up to 90m/s may be achievable. As with bows, the ST of the user is important more for how heavy a projectile can be launched to those speeds than for determining the velocity itself. With slings, however, that's not determined primarily by material properties and design principles (although these are important), they are skill dependant. That argues that untrained use of the Sling ought to suffer damage penalties and that Perks to improve performance, much like Strongbow, ought to be available.

Aside from other considerations, it seems to me that 28g-40g glandes are probably more economical than effective, with heavier glandes being much more likely to wound and kill humans and larger animals. A 36g glans can be lethal, yes, but a more important consideration is that you can obtain more of them for the same amount of lead than you can make of more lethal 62g or 100-120g ones.

The reason we find a lot of those small glandes is that in most historical warfare, something that did 1d(0.5) cr was a scary enough weapon and it was better to put more of those in the air than try for 1d+2 cr at the cost of spending x4 as much and having to carry x4 as heavy ammunition. Adventurers in GURPS may feel differently.

Re: Slings, realistic physics, The Deadly Spring
 

We do already have proposed options that do a bit about the sw/thr damage issue, remember. Not from a 'do the physics' perspective, but still, any mismatch will be smaller.

Re: Slings, realistic physics, The Deadly Spring
 

Even for those of us who are fine with the standard GURPS damage tables for melee weapons, the sling at ST 14 generates 2d pi damage. Without a reasonable AD, such as the aforementioned (.5), I think that creates a bit of an issue with suspension of disbelief. Sure, ST 14 is very strong, but that damage is 7 points of penetration...that'll get through all chainmail ever made. I just don't see that happening. With the (.5) AD tacked on, this doesn't happen. I have less issue with the sling going through leather, though even that is probably unlikely.

But, at the end of the day, either these weapons were useful or they weren't. We know they were used. We also know armor was used. And more importantly, in play we know that PCs and enemies will wear armor (perhaps even ahistorical levels of armor), and there's frankly no good gameplay reason to nerf muscle powered weapons down to no effective damage.

Edit: Here's a thought, maybe rather than a straight up (.5) AD, we apply the "edge protection" rule to sling bullets. Basically, if they can't penetrate, they can still do crushing damage, which I find much more believable.

Re: Slings, realistic physics, The Deadly Spring
 

According to models designed by the US Armed Forces to model bullet penetration, even the world records of slinging with a 28g to 51g bullets would not have penetrated winter clothing at point blank range. GURPS assumes 28g sling ammunition, which I'm comfortable saying will never penetrate DR 1 armour at human ST scales, except on a critical hit.

Sling damage is not pi and cannot be modelled as pi. It's crushing damage and while it can be lethal to unarmoured people, for the most part, like arrows, even a solid hit will tend to wound and not kill a human.

Re: Slings, realistic physics, The Deadly Spring
 

It's not clear why slings in 4e do piercing damage to start with, the evidence for slingers targeting eyes or vitals is pretty thin, and in general it appears that slings killed without making holes in people (the enemy dies from the blow of the stone without the loss of any blood).

Re: Slings, realistic physics, The Deadly Spring
 

I'd be inclined to call it crushing and then be done with it then in my games. Piercing for slings is probably the strange part. And I have no trouble believing that a ST 14 person firing a sling stone for 7 damage will do some damage to a guy in chainmail. Maybe not 5 damage, but 3 for sure.

Re: Slings, realistic physics, The Deadly Spring
 

That's nearly a broken arm covered in metal armor. Now that seems a might silly for any rock slung by humans not named David.

Re: Slings, realistic physics, The Deadly Spring
 

I think a (.5) AD solves that nicely (because I do not disagree). Alternately, slings could be sw-2 damage or something. I tend to prefer the (.5) AD for stones and maybe lead shot.

If it's pi, ironically, the metal armor does better--DR 4 instead of 2.

Re: Slings, realistic physics, The Deadly Spring
 

A lot of the disconnect is because the higher ST guy is still using ammunition of the same weight. That doesn't fit with reality, where a 28g projectile is not going to hurt anyone wearing padded mail, no matter who propels it.

The strong guy, however, can use heavier projectiles without losing too much velocity. That's the advantage.

And with ST 14, he ought to be able to use 1-lb stones or even 1-lb lead glandes. And those can hurt at 45+ m/s.

Sling projectile types, weight and other musings
 

As a quick-and-dirty fix, I plan to have sling projectiles affect the stats somewhat more than they do.

The basic stats, whatever they end up being, represent picked stones of the appropriate weight. Every individual slinger and sling combination will have different prefered weights, but in general, in order to get a higher damage from higher ST, it's necessary to use heavier projectiles. Sling length will similarly be dependent on the individual slinger, but tend to be longer to make use of higher ST.

Using a higher or lower weight projectile than your optimum will reduce Acc, Range and/or damage, though it can be a valid strategy to use much heavier projectiles than you get your best ranges with, in order to get more damage at short range.

As long as I include an AD and have damage be crushing, not to mention require heavier projectiles for increased damage, there's no obvious reason why the Range and Dmg listed for the sling in LT can't be used until something better comes along. I don't object to terrible wounding, as long as it doesn't penetrate much better than in reality.

I guess that a typical rock has AD(0.25) against any kind of rigid armour harder than rock* or any metal armour and AD(1/3) otherwise.

Edit: This represents poor penetration and performacne in general against any kind of proper armour, i.e. external to the target, with padding and suchlike. If the DR is instead part of the target, such as when damaging shields or vehicles, all ADs for sling projectiles ought to be improved by two steps, to the maximum of AD(1).

The steps are AD (0.1), AD (0.2), AD(0.25), AD(1/3), AD(0.5), AD(2/3) and AD(1), or slightlly more steps than are in the regular progression, to allow for more fine-tuned performance.

I'm thinking that sw cr represents a rock of ca 0.06-0.1 lbs. for a normal character, ST 8-12. Range x6/x10 is okay for that, but given that a 51g rock has been slung 475m or so, there ought to be some way to reach further.

An alternate mode of use that requires time for set-up, can only be done as an All-Out Attack and uses a very high arc, for a penalty to hit?

I could see 1-second set-up allowing +50% Max Range, i.e. Range x6/x15 for a typical sling, for a -2 to hit and 2-second set-up allowing x2 Max Range, i.e. Range x6/x20, for a -5 to hit. All-Out Attack (Strong) would add +1/3 to Max Range in addition to adding to damage.

I suppose that a prerequisite for such dramatic improvements would be having a fairly long sling, i.e. 4-5 feet and/or a staff sling. With only a regular length sling and normal weight projectiles, the maximum increase in distance would probably be a 1-second set-up followed by an All-Out Attack (Strong), totalling something like a +50% Max Range and -2 to hit.

If I come up with something to make the length of slings affect base stats, I'd have to rework the percentage of improvements possible.

The lighter rocks of 0.05 lbs. would be too light for optimal damage at ST 10+ and instead represent a cheap and handy type of harassment ammunition. Give ammunition of ca 2/3 weight -1 per two die to damage and disallow boosting range beyond +50% with a high arc and set-up, as it lacks enough heft for it. Ammunition of half the weight required for your ST gives -1/die damage and cannot benefit from boosting range at all, except the +1/3 from All-Out Attack (Strong).

Ammunition that weighs 100% more than your ST requires would give +1 per two die to damage, at the cost of reducing Max Range by 20%. Range x6/x8.

Very heavy projectiles, like those used for LT's Heavy Sling, are possible. Ammunition that is around 500% of the basic projectile weight for your ST would give -2 to skill against point targets (but not if aimed at a hex) and reduce Max Range to the same as 1/2 Range, i.e. Range x6/x6, but give +1/die to damage.

Projectiles are assumed to be chosen for aerodynamic properties. If not, reduce ranges down to x4/x6 for unwieldy rocks of the standard size, x4/x5 for heavier ones and x4/x4 for very heavy ones. Maximum Range can be boosted as above, more or less regardless of projectile type.

Density is important to range and damage both.

Fired clay and similar projectiles will generally be light, but this is not required, as long as the sling has a large enough pouch for the projectile. In addition to any modifications for weight, fired clay or other projectiles of similar density receive -1 to damage per die and has Range 4x/x8 for standard weight ones. They fragment on impact with anything remotely hard, which means AD is (0.1) against any rigid armour harder than fired clay as well as any metal armour, AD(0.2) otherwise.

On the other hand, the use of fired clay allows projectiles to be shaped in a perfect aerodynamic shape, which for slinging techniques usually means biconical or ovoid, much like an American football. This gives Range x5/x10 and only -1 per two dice damage. Since it impacts end-on, it also helps penetration, despite usually fragmenting against the target. AD (0.2) against metal armour and rigid armour harder than fired clay and AD(0.25) otherwise. The predictable shape and weight also gives +1 to Acc.

If anyone bothers to cut stone into similar aerodynamic shape, it gets +1 per two dice of damage, Range x8/x12 and AD(0.33) against rigid armour harder than stone or any metal armour and AD(0.5) otherwise. It gets the same +1 to Acc.

Lead was consistently the favourite material for war projectiles of sling-using cultures that had access to it. A lead projectile of the same weight as a stone, with a similar design, will be much smaller. This gives +1 per two dice to damage and Range x10/x15. It has AD(0.33) against any metal armour or rigid armour made from harder materials and AD(0.5) otherwise.

Lead is usually formed into aerodynamic biconical or ovoid shapes, which gives +1 per die to damage, Range x12/x18 and AD (0.5) against metal or rigid armour made from harder materials and AD(0.67) otherwise. This also gives +1 to Acc.

Edit: At longer ranges, it becomes important to use rules analogous to the Bullet Travel time in TS. In addition, penetration also goes down at longer ranges, even beyond what the reduction of kinetic energy and momentum would indicate, because the projectile is likely to strike from an angle above. To simulate this, reduce AD by one step at at distances beyond 25% of Maximum Range. This does not apply to very heavy projectiles (500% weight), which have a different penetration and wounding mechanism, relying more on momentum.

*With the caveat that the rigid armour in question must be thick and heavy enough compared to the projectile to actually count as armour and not just a part of the target that's treated as DR. Glass windows may have DR 1, but that's not rigid armour for these purposes. Thick glass casing with DR 3 usually would be, though, unless the projectile is very big. So far, this is a GM's judgment call, but eventually, I hope to have a definable rule for it.