signal beam = no... With jirachi's amazing movepool, there are better options. Thunderbolt, Psychic, HP [Ground], or HP [Fire] are all better options.
Thunderbolt for gyarados and bulky waters, Psychic for a STAB move that isn't resisted by 1/2 of the pokemon out there, HP [Ground] for the steels, specifically heatran that can switch into this set without much worry, and HP [Fire] for the same as the last reason, but for Scizor this time.