Go to [FSX]\SimObjects\Misc\CS_Weapon_XXX\ (where xxx = weapon name), in there you will find a file named sim.cfg with all the information there.

[fltsim.0]
title=CS_Weapon_Hydra70
model=
texture=

[General]
category=SimpleObject

[contact_points]
destroy_on_impact=1

[effects]
ImpactLand  = csweapon_rocket_land
ImpactWater = csweapon_rocket_water1

The effects themselves are in the [FSX]\Effects\ folder

Mark