Here is my advice (I am running a 4th Level Human (Taldor) Guntank in the Kimgmaker Campaign): Do it. This far, I am running one of the most powerful characters in the campaign. I have 2 more AC values than our Paladin (8 more than the Monk, and a whopping 12 more than the ranger.) While the Paladin probably deals the most damage in our Party, I deal reliable damage (Don't go with an axe musket, stick with a regular musket and your hand weapon of choice + non-tower shield, my DM made a ruling that you can shoot with you trigger finger in your shield hand, as long as it is not a tower shield (The specific rule in the book says that while using a tower shield you can not do things that you could with smaller shields [i.e. holding torches, pulling levers, holding your horses reins]) with a +9 hit chance and d12 damage (You do not start adding Dex into damage rolls until level 5 with Gunmastery [Also, whoever said you lose Gunmastery for Armormastery is a fool, you lose Nimble for it-- This isn't so bad as if you notice, for every point in armor mastery you have, you lose 1 rank of check penalty and gain 1 max Dex level, this combined with armor traits and feats makes a great combo]). Now with feats and traits and class features, you start losing max Dex levels, making it so you are dealing 10 to 12 damage average with a non-crit upwards in the 23 area. (The highest I've done criting was on a troll and that was 46 [12+12+10+12] and that is without adding Dex or enchanted weapons, that was my dingy starter firearms.) Gunslingers are my favorite class, and if you want a knight with a gun, definitally go Gunslinger.
