Shades of Green said:
The issue at hand is my desire to integrate certain Steampunk elemnts into my campaign, centered around the technically-advanced Humano-Dwarven empire. While this won't include extreme steampunk (full-blown sentient Analytical Engines), this will include steam-powered vehicles (ships and trains, but to a very limited degree in the Renyan frontier) and, among other things, possibly firearms.
My question is: How unbalancing flintlock pistols/musketes are to the game world, and how deeply they ill effect warfare (i.e. how much weapons/armor will be outdated). I wish to create a feel similar to the later Age of Sail with the first few steps of the industrial revolution (and steampunk/clockwork tech) taking place.
First of all, I've played Great Age of Sail campaigns completely without gunpowder. If you are willing to suspend some disbelief, magonels make perfectly acceptable cannons and crossbows make perfectly acceptable muskets.
This depends entirely on how significant you wish to make firearms to the campaign when you model them. Firearms didn't obselete longbows until the 18th century. The main advantage of a firearm is that it didn't take a lifetime of training to get someone who had a reasonable chance of hitting the target. Firearms didn't obselete melee weapons until near the end of the 19th century (arguably during the American Civil war, though most commanders of the time didn't yet realize it and many European commanders wouldn't be convinced of it until well into WWI.)
On the low/simple side of things, you could make Firearms simply a slightly improved crossbow much in the way that bastard sword is a slightly improved long sword and dwarven war axe is merely a slightly improved battle axe. Simply make Pistol and Rifle exotic weapon proficiencies, and increase the dice of damage by 1 step. So a 'pistol' is a medium crossbow that does 1d10 damage, and a musket is a heavy crossbow that does 1d12 damage. If you like, you can make reloading these weapons full round actions. If you do this, not only will the presence of firearms not unbalance the campaign, but they'll likely be weak enough that no one in the party will use them.
More realistically, you can do the above BUT make pistols and rifle's simple weapons. This will make them ubiquitous in the campaign, but still won't imbalance it. If you really want to go this route and make the weapons common but not overly powerful, make longbows and slings into an exotic weapons to reflect the extra training that goes into using them. Now you'll have longbows and slings relatively rare, but everyone can tote around a musket.
Going further down this line, the real advantage of muskets over bows wasn't increased range - it was increased penetrating power. Allow firearms (and maybe heavy crossbows) to have a penetration score of up to +3 (at least in this period). The penetration score reduces the effective armor of a target by up to that number. For instance a target in chain (armor bonus +5) would have have an effective AC of only 14 vs a flintlock pistol or 12 vs. a flintlock musket, rather than the usual 15. Of course, you can only fire every other turn or three, but low level mooks get a big improvement in thier chances to hit armored opponents.
Going even further, firearms are easier to aim compared to bows, so you might add a +1 (for a musket) or +2 (for a kentucky rifle) accuracy bonus when firing a firearm.
Going even further, musket balls wreck havoc with living flesh compared to an arrow. You might make firearms have a critical range of 19-20(x3). By this time, firearms will have started to make your campaign far more lethal, but won't really have made things any better for your average PC's because the reload time makes them rather cumbersome for your average heroes. I've suggested a full round reload action, but in point of fact its probably closer to 10 rounds for most period muskets and _longer_ for most period pistols. You could have feats like 'Musketeer' to reduce the reload action by 3 rounds or so (never less than a round), or 'Veteren Musketeer' to reduce it by a further 3 rounds, or whatever but the point is that firearms are likely to remain primarily of benefit to the NPC's and not the PC's. A sqaud of 20 goblins armed with muskets is a serious problem, if effectively the goblins now have a weapon that gives them +4 to hit and does 1d12 damage with a critical range of 19-20(x3). Even if the muskets are dropped after one volley, the PC's have probably been blooded well beyond what 20 goblins would normally be able to do to them.