The Quest marker, from First Endeavor Paintball, was spawned around similar 03/04 timeframe as the current Shocker SFT markers. It features a reasonably simplistic design combined with some tried-and-tested methods for support features (detents, eyes, trigger, etc). The marker isn't considered super-modern like some products developed in 2007-2008, but can still hold its own, just as a Shocker can.
Member Gen was good enough to produce this diagram, alongside with his Quest animation.
Below is a diagram of the 4B firing assembly. Its o-rings are the same as the factory bolts, with the obvious addition of the forward and rearward bumers.