With the chamber loaded I can pull the slide back and eject the round, does this mean the action is not locking closed?

The Gold Rush Rifle and Carbine are of a "locked" breech design. When you have moved the pump arm fully forward, the arm assembly causes the locking brace to engage the breech bolt. Pressure against the breech bolt face will not move it rearward. When you pull the pump arm back slightly, the locking brace disengages the breech bolt and further pump arm movement will begin to open the breech.

The Gold Rush design does not incorporate a slide or pump arm lock that must be manually depressed to retract the breech bolt, as some other pump operated firearms do.