Magnum Takedown

I am working on a Gamo Swarm Magnum Gen 1 and I cannot figure out how to take the piston out. I removed the pin at the rear along with the trigger group, only to find that there is another pin further down the action that is actually holding the piston. I tried banging it out with a punch and hammer to no avail, so I took it to the vice to try and press it out. No luck. I noticed that on one end of the pin there are two circular slots offset from the center, so I figure maybe I should put pliers in there and thread it out. Again, nothing. I looked inside the from the back of the gun and I cannot see any threading on the pin anyway. And I did my best to take the preload off the pin as well, using a locking clamp and a carved bit of wood shaped to fit into the action and around the pin. Long story short nothing is working.