Reducing melee weapon weight

[z0boson]

Hello!

Pyramid 3/51 (Tech & Toys III) introduces a Nanomaterial option that halves melee weapon weight (A similar option could be used in Fantasy settings for Mithril and other exotic material weapons). However, there are no stat changes given. Shouldn't min ST be reduced? Maybe damage? How realistic is this option? Doesn't the reduced weight impact the performance of the weapon?

Thank you for your ideas!

[DanHoward]

Reduced weight should reduce swinging damage but thrusting damage probably won't be affected.

[z0boson]

Originally Posted by DanHoward

Reduced weight should reduce swinging damage but thrusting damage probably won't be affected.

Thank you for your quick reply. I guess the best way to figure out min ST is to use the table provided on page 16 of Low-Tech companion 2?

[Polydamas]

Originally Posted by DanHoward

Reduced weight should reduce swinging damage but thrusting damage probably won't be affected.

I would also insist on using A Matter of Inches and Beats from Martial Arts. Lightness in hand weapons is not always a good thing.

[Anthony]

Originally Posted by DanHoward

Reduced weight should reduce swinging damage but thrusting damage probably won't be affected.

Unclear; depends how much thrusting damage is based on the kinetic energy of the weapon itself, vs energy transfer from your arm and body. Realistically, I think the energy transfer from arm and body mostly only happens if you penetrate armor.

[nick012000]

I'll point out with advanced nanomaterials or magical materials like mithril, it's entirely possible that the slightly-reduced damage from weighing less is counteracted by a slight bonus from the quality of the material (e.g. sharpness and ability to hold an edge, assorted minor magical effects, whatever).

[gilbertocarlos]

Remember however that GURPS Low-tech weapons are heavier than real world ones.
An axe weights 4lbs in GURPS, a combat axe IRL almost never reaches 3lbs.
A broadsword weights 3lbs in GURPS, a sword IRL is around 2lbs.
A halberd weights 10lbs in GURPS, real life ones are around 6lbs.

[Polydamas]

Originally Posted by Anthony

Unclear; depends how much thrusting damage is based on the kinetic energy of the weapon itself, vs energy transfer from your arm and body. Realistically, I think the energy transfer from arm and body mostly only happens if you penetrate armor.

Horsfal et al. disagree; their knife had more KE than the mass and velocity of the knife predicted. (In my experience, there is a big difference between a thrust which is properly supported by the body, and one which is fast but not supported). In any case, I have never seen serious KE measurements for weapons of different weight used by the same person. Horsfal et al. just tested one knife used overhand and underhand.

Originally Posted by gilbertocarlos

Remember however that GURPS Low-tech weapons are heavier than real world ones.
An axe weights 4lbs in GURPS, a combat axe IRL almost never reaches 3lbs.
A broadsword weights 3lbs in GURPS, a sword IRL is around 2lbs.
A halberd weights 10lbs in GURPS, real life ones are around 6lbs.

That was true in the Basic Set, but according to MA and LT, the Axe is a huge job which should really be used two-handed, the Broadsword includes the belt and scabbard, and the Halberd has been depreciated for weapons built around lighter polearms. Now this is a bit more complex ...

[Varyon]

Originally Posted by Anthony

Unclear; depends how much thrusting damage is based on the kinetic energy of the weapon itself, vs energy transfer from your arm and body. Realistically, I think the energy transfer from arm and body mostly only happens if you penetrate armor.

I think it depends heavily on the weight of the weapon. For light weapons, the effect of weapon weight is outdone by the weight the person is putting into the strike (fist loads improve damage by serving as or making the hand into a more efficient striking surface). For heavy weapons, weapon weight does matter, but only up to a point, as eventually you'll hit a weight where your muscles hit their peak and thus cannot impart any more kinetic energy into the strike.

The simplest solution is what Dan has suggested - no effect on thrusting damage. Alternatively, take the weight of the character's arm (~5% character weight; if the character has Striking ST, Arm ST, etc, you may want to use a higher base weight) and add in the weight of the normal weapon. This is the default "striking weight." Now work out the heavier/lighter weapon's "striking weight," divide it by the original, and take the square root of it. If the weapon had a +1 or better damage bonus, this is the multiplier for it; if it's 0 or less, just use that column from LTC2. You may wish to cap out the total weight to represent the muscles hitting their peak; 1.5x weight might be appropriate (so for a 200 lb character, he hits his peak at 15 lb striking weight).
Note you aren't likely to get much of an effect - for a 200 lb character, going from a theoretical weightless weapon with a +3 damage bonus to a 5-lb version of the same (character's maximum) changes that +3 to a +4 (+3.66) - were that bonus instead a +2, there would be no change (+2.44). For simplicity, I'd say stick with Dan's advice.

As for swing damage, that's a horse of a different color. In that case, weapon weight is striking weight, so multiply by the square root of the weight multiplier (or use the chart from LTC2). A thrusting broadsword (sw+1 cut, thr+2 imp) made of orichalcum (1/3 weight) would have its swing damage multiplied by the square root of 1/3, or .58, which results in no change (+1*.58=+.58, which rounds up to +1). Wielded by a 200 lb character, it goes from a striking weight of 13 lb to a striking weight of 11 lb, for a .85 multiplier; the square root of this is .92, so no change there either (+2*.92=+1.8, which rounds up to +2).
MinST for the weapon is 5 (less than 2 lb means 6, but blades typically have a slightly lower MinST, and this is right at the breakpoint between 5 and 6). Its breakage properties depend on how the GM envisions orichalcum - it should probably use its original (3 lb) weight, at a minimum.

[z0boson]

Originally Posted by Varyon

I think it depends heavily on the weight of the weapon. For light weapons, the effect of weapon weight is outdone by the weight the person is putting into the strike (fist loads improve damage by serving as or making the hand into a more efficient striking surface). For heavy weapons, weapon weight does matter, but only up to a point, as eventually you'll hit a weight where your muscles hit their peak and thus cannot impart any more kinetic energy into the strike.

The simplest solution is what Dan has suggested - no effect on thrusting damage. Alternatively, take the weight of the character's arm (~5% character weight; if the character has Striking ST, Arm ST, etc, you may want to use a higher base weight) and add in the weight of the normal weapon. This is the default "striking weight." Now work out the heavier/lighter weapon's "striking weight," divide it by the original, and take the square root of it. If the weapon had a +1 or better damage bonus, this is the multiplier for it; if it's 0 or less, just use that column from LTC2. You may wish to cap out the total weight to represent the muscles hitting their peak; 1.5x weight might be appropriate (so for a 200 lb character, he hits his peak at 15 lb striking weight).
Note you aren't likely to get much of an effect - for a 200 lb character, going from a theoretical weightless weapon with a +3 damage bonus to a 5-lb version of the same (character's maximum) changes that +3 to a +4 (+3.66) - were that bonus instead a +2, there would be no change (+2.44). For simplicity, I'd say stick with Dan's advice.

As for swing damage, that's a horse of a different color. In that case, weapon weight is striking weight, so multiply by the square root of the weight multiplier (or use the chart from LTC2). A thrusting broadsword (sw+1 cut, thr+2 imp) made of orichalcum (1/3 weight) would have its swing damage multiplied by the square root of 1/3, or .58, which results in no change (+1*.58=+.58, which rounds up to +1). Wielded by a 200 lb character, it goes from a striking weight of 13 lb to a striking weight of 11 lb, for a .85 multiplier; the square root of this is .92, so no change there either (+2*.92=+1.8, which rounds up to +2).
MinST for the weapon is 5 (less than 2 lb means 6, but blades typically have a slightly lower MinST, and this is right at the breakpoint between 5 and 6). Its breakage properties depend on how the GM envisions orichalcum - it should probably use its original (3 lb) weight, at a minimum.

Thank you for the advice - this is indeed a good formula to get an idea of the order of magnitude of the effect. This means that light weapons don't suffer much from a further reduction in weight, while heavier (swing) weapons are better left to their original weight. I guess that makes sense because this is the reason they were designed with more mass in the first place. I would also imagine that swing weapons with the center of mass close to the striking point (like hammers) are more affected than weapons with the CoM closer to the wielders hand (like swords). But this effect is probably already taken into account by their higher swing damage modifier.