Since the rule for multiple archetypes is that they can't replace or change the same class feature, for the gunslinger can you take the gun scavenger and musket master archetypes together? The reason to do this would be to use the "change out" deed from gun scavenger and still be able to reload two-handed firearms quickly with musket master. The ability to turn a musket into a scatter weapon, with a much longer cone and better damage than the blunderbuss or dragon pistol, seems pretty strong. A 1d12 touch attack in a 40 foot cone at level 1! Eventually I would carry two muskets, one for single targets and one for scatter. When the scatter weapon misfires, as long as you have a grit point, just take a full-round action to remove the broken condition and reapply the scatter weapon quality.
The reason I'm not sure you can take both archetypes is the archetype table at http://www.d20pfsrd.com/classes/base-classes/gunslinger. It says that musket master replaces the nimble feature which is probably an error, since none of the features listed on the musket master page do that. It also says that musket master and gun scavenger both change the weapon & armor class feature. Musket master does, since it makes you only proficient with 2-handed firearms, but it's debatable whether gun scavenger does too. You could argue that the "go by feel" ability does. What do people think?
Even if you can't take both archetypes, level 1 gun scavenger seems like a pretty good dip to get a nice scatter weapon. If you're not concerned about getting multiple shots in a turn, you could just buy a beneficial bandolier and reload one bullet as a swift action each round. No need to take the rapid reload feat or use alchemical cartridges.