The Witch Hunters FAQ covers this question quite nicely:
Righteous Fury (p. 27): The rules for priests state that the unit always counts as moving, and must always charge. To clarify, this rule effectively means that units with an attached Priest may never fire a Rapid Fire weapon if they are within charge range of an enemy, as to do so would preclude them from charging. If there are no enemies within charge range, they can still fire at targets up to 12" away, but not beyond, as they always count as moving.