I've been running Rpg games for a long time now. Pathfinder is nice in certain aspects. It is always good to ask your GM about bringing a revolver in.... However I'm on the revolver = pistol side of the rules and the reasons are as follows.
Historically speaking the worlds first revolver was made in 1597 by Hans Stropler. It is an 8 shot flintlock revolver. If you notice the end of the handle is a large heavy ball. When you are done with your shots and/or your opponent comes into hand to hand combat, the revolver becomes a club.
This is what I use for reference of a revolver in a fantasy setting.
Incredibly rare, incredibly expensive to make, but a valid weapon to be used. There is no real reason why not having this kind of weapon when you have have Maces of Disruption, Luck Swords, etc, etc, that are far more powerful than this. Magic still rules the day.
As far as size of the pistol (compared to the revolver) of that day? Almost the same. Including the Ball/club in the end of the handle. The youtube video gives you a small history about the Hans Stropler revolver.
The next url is a similar picture of a single shot variety of pistol.
Bty both pistols featured in that article definitely are not the ones used in the assassination of a monarch.
Both firearms were made for high class/nobility. Common weapons for this time period was basic in its construction and definitely not as ornate. And were single shot.
That's my take. A little bit of history can go well in a fantasy setting. I have used it in a character and allowed it as a GM if the character is high enough level to logically purchase one.
In the end it really depends on the GM to make the decision one way or another.