Should last a really long time, if there are no leaks in it. Compare them to gas pistons that lift up a hatch on a car or minivan. Those are constantly under pressure for days on end, until someone opens up the hatch. Same thing with the gas ram in your gun. They'll allow you to leave the gun cocked for long periods of time until you're ready to fire, without any loss of speed. They're also less susceptible to damage from using too light of a pellet, whereas a spring can bend or break. I'm not entirely sure of the lifespan of the gas rams. Someone else here with more experience with them would be better able to tell you.