The firing range is a facility on Galactica that allows her crew to maintain their small arms proficiency.
After Sharon Valerii is revealed to be a Cylon sleeper agent, some of the crew post images of her face on the targets in Galactica's (Flight of the Phoenix).
Apollo and Starbuck are conducting target practice on the firing range when the oxygen to the room reaches dangerously low levels. They overcome their hypoxic delirium long enough to shoot out the glass of the pressurized door, allowing air to reach them. The drop in air pressure was apparently caused by the effects of the Cylon logic bomb (Flight of the Phoenix).