[Peter von Kleinsmid]

Yes, quite. It doesn't say how much of the weight is powder, and a grenade is also filled with scrap metal, so I'd say it's definitely not a pound of powder.

Also, TFT weights are mainly for determining encumbrance, not for highly accurate comparisons to real-world objects. If all the weights were carefully revised to match actual real-world weights, it would create a need for a new encumbrance system that wasn't based on weight.