Ok... Let me clear this up since these guys don't know wut they are talking about
You Can use Co2 on the Shocker. It's highley frowned apon due to the fact that it's bad for the gun becuase it can freeze it up, And it will break the internal o-rings all the time.
If you do not own a HPA tank then i sugest you buy an impulse. But i wouldn't really recomend the Freak Factory, this is b/c most "factory" impulses are usualy a rip off for just some milling. this is especially true for the Freak Factory.
You might wana look into a Nasty Impulse, or just a Standard base impulse and upgrade it. there are links to Wolverines site in the FAQ stickies at the top of the page.
you might also wana try
www.impulseownersgroup.com for some more help and FAQ's