I haven’t found any rules related to this subject. Nothing about weight changing the damage of any weapon was seen anywhere, and neither was there anything on the improvised weapon.
Have anyone seen house rules that modified the damage of standard weapons that happen to be extremely heavy by design? Like instead of using a Warhammer weighing 2lbs someone wants to use one that is 20lbs.
Using everyday items that are not included in the official list of weapons are generally counted as attacking with an improvised weapon, like a chair or a wine bottle. But the problem is, what if the improvised weapon in question is so ridiculously heavy that it no longer makes logical sense for it to only inflict 1d4 damage?
Consider The Bag of Holding, which will always be 15lbs. (For reference, a battleax is weighed at 8lbs and heavy crossbow weighs 18lbs) Even if the texture of the bag in question is soft leather, when you swing that bag to hit someone or someone, the weight and momentum itself should be plenty enough to crush things.
PS: Not that I would want to swing that thing around! Damaging the bag could be disastrous.
Swinging around a sack with a rock is definitely an improvised weapon with 1d4 damage. But if someone swings a regular sack filled with a lot of rocks (or with tons of loot and gold),filled the bag with more than 50lbs worth of stuff and swung it around? Or 100lbs? (Assuming the sack doesn’t rip or fall apart before the smashing hit connects).
Speaking of which, would using a gigantic heavy table that is capable of seating twenty people as an improvised weapon during the bar fight in the tavern really only do 1d4 damage?