Since a bullets behavior is fairly simple (Just moves forward with a certain velocity until it hits something, then spawn some particles and then die.) and since you want them moving at a low velocity, I would recommend just using an Area node.
Two know when it hits something you just the
body_entered signals to a method that spawns a particle system for the fire effects and the queue free the bullet.
Also it doesn't make much of a difference if you use a kinematic body instead.