PKD:
I agree with the other posters; you can load both per the diagram that shows two barrels. In fact, both could be loaded at the same time all the time, but after the .222 is fired, you need to use a turn to reload that round.
Cover in a Chase:
As for cover, technically yes, the prey could go for cover. The Chase Maneuver for that is called "Other". It would do exactly as the other poster stated, slow them down, thus they do not get to increase range, but then if the Pursuer is standing and shooting, they will not be closing range. The GM could decide at a point like this to take the combat out of chase mode and drop back onto map or just "theatre of the mind" as mentioned on page 64.
They could also do a Stand and Shoot as their own Chase Maneuver which is conducted as a "normal ranged attack", taking cover as a free action in tandem with that attack. Rules don't say can or cannot do that one as part of that Chase Maneuver, but I would allow it.
There are better defensive Chase Maneuvers though then just costing the Pursuer a single disadvantage base die removal due to Prey cover; They could chose "Hide" and have a chance of just winning the chase outright or getting the drop on the Pursuer to kill them. They could "Block" which is like cover but instead of costing them one die for cover, it would cost them ALL dice due to losing their entire maneuver! All of this before the Pursuer even gets their roll.
The catch is that Prey needs to make those rolls and the Pursuer needs to fail
:
Hide= Stealth vs. Observation
Block = Prey Succeeds Force roll and then after Pursuer Fails Force roll.