There's a weapon introduced in the second appendix of the Red Hand of Doom adventure book called a "Dragonchain"
It is a bludgeoning/trip/disarm weapon that has text which states that if you enter a grapple, you can wrap the chain around your opponent and deal automatic constrict damage on a successful grapple check to the tune of 1d8+Str*1.5
What happens if you have constrict from another source? Like if a Warblade has this weapon and is in the Crushing Weight of the Mountain stance, which says you deal 2d6+Str*1.5 damage on a successful check?
Do they stack, or do you only use the bigger source?