There is no tougher job for a spring than driving a magnum spring gun piston. In no other mechanism is a spring compressed to coil bind,then released with little resistance to expand freely.Even the valve springs in a racebike engine are under lower stress,and they may get changed every race.Before the magnum sprigner became the norm,spring were expected to last for years,(or decades),and did,mostly because of slower piston speeds. Springs in old match rifles will last 100's of 1,000's of shots. Consider the mainspring in your magnum a "consumeable",like the air cleaner and tires on your car.