using pneumatics as rubber bands

has anyone ever used a piston as a rubber band that is not hooked up to a tank or solenoid? was it very successful?

By plugging the end, do you mean? I haven’t specifically tried that, but from playing with pneumatics with a valve closed or hose crimped I wouldn’t imagine this is very effective at all, as there is very little springy-ness in them from just the small amount of air pressure created. Not to mention that the pneumatic cylinder takes up a ton of room for only 2" of movement, something a significantly smaller rubber band will do much better.

the idea being that the piston would be pressured one way

The force of the piston would be non linear. If the only air supply was the air in the piston then there would be double the force after you push it halfway. It would be perfectly exponential which is usually not what you are looking for. You would need a dedicated tank or similar storage supply so that you were not storing the same amount of air in 1/2 the volume or the same amount of air in 0 volume.

(volume not being compressed + volume being compressed)/(volume not being compressed) would be the multiple of the force at the end and beginning of the stroke

If the volume of both was 1 then the piston fully retracted would have twice the pressure(which is linear in relation to force).
If the volume of not being compressed was 0 then the force would be infinite to compress any farther.

ok that makes sense, my thinking is that if the piston and tubing, needed to go to connectors, is set to a point that when the piston is completely expanded/contracted and the connections would do not blow out that the piston could provide a relatively explosive force