Is it possible to use OnCollisionEnter or detect collision otherwise without having one object affect the position of the other?
i.e., bullet A hits Object B, but Object B does not move, bullet A goes "right through"
OnTriggerEnter with isTrigger checkboxed for the bullet and rigidbody set for both objects:
you can set for the GameObjects that are Colliding in the Collider component settings in the inspector "is Trigger = true" and call OnTriggerEnter instead of OnCollisionEnter ... so the colliders will "fly" or go through each other.
so this way Bullet A hits Object B, and Object B does not Move, Bullet A goes through :)
also, try to debug yor collition/trigger