hey guys tried this a while ago. since its basically expanding glue it wont work.
in theory, if you do it like injection molding and have many point on where you will inject the foam. use low expansion and have other points where the excess can escape. its possible. b
but you wont be able to use it for mold making. only to stiffen the pep'd weapon.
i have used it on plastic airsoft shells and it has cracked some of them.
good luck guys