Actually, IDPA has concluded that a magazine disconnect is not a "safety" in the usual sense of the word or normal use of the gun and may be deleted. From the Rules Clarification section of the IDPA board:
There is precedence in other action shooting sports for a magazine disconnector to not be considered a safety. Trigger reliability work and trigger replacement is currently allowed for ESP & CDP. Several aftermarket trigger kits have no magazine disconnector or any capability of accepting a disconnector. Based on this information, the rules clarification committee has ruled that a magazine disconnector is not a safety and can be removed as part of trigger reliability enhancements."
I know how to get the magazine disconnect out of a Browning or a S&W but not a Ruger.