[Lupo]

Sheaths cause a lot of trouble if you use the 1/3 - 20% rules.

In our campaigns, we just assume that the weight and cost of Sheaths are negligible, and that characters always have appropriate sheaths for their weapons (unless, of course, they just escaped from prison or something).

And, if for some reason I really wanted to be detailed and accurate about sheaths, I'd rule that they weigh 1 lb and cost $50, in addition to the weapon (in order to avoid all the recalculations and weird stuff that happens if you mess with listed weapon costs and weights).

I never understood why GURPS went into so much trouble just for accounting for sheaths.