Its a standard action to reload a single one handed firearm barrel.
Rapid Reload makes this a move action and alchemical cartridges reduces this to a free action.
A pepperbox has 6 barrels, is this a single free action, or 6 free actions? If 6 free actions, is that a move-equivalent action? a standard-equivalent? Without alchemical cartridges, is it 6 move actions, or 1 move actions?
I'm of the opinion that a full-round action should re-load all the barrels, but I'm hardily the expert. I've seen answers that are basically "GM's Discretion" under the general feed, but I was wondering if there was a society rule somewhere.
GM discretion is the general rule for defining a reasonable number of free actions in a round. Reloading a pepperbox would be 6 free actions. My personal opinion is that this is not any more unreasonable in one round than allowing enough reloads for a high level gunslinger to complete a hasted rapid shot round.
That said, I am building a musket master gunslinger around the vital strike tree because I have a hard time wrapping my head around reloading a musket enough times to rapid shot.