Reducing melee weapon weight

[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.