You're real deep into the area of personal preference on this one. Both coil springs and gas springs have advantages and disadvantages. I've had both and find I prefer a coil spring. You may not. A new gas spring would be a drop in replacement, obviously. Replacing it with a coil spring you'd need to identify your choice of spring then obtain a spring guide to hold it straight while cocking. Your initial coil spring will take some measurement and a bit of planning. Your choice of a spring will affect the power and "shootability" of the gun.