Since I'm pretty sure this got posted on the 'House Rules' forum for feedback at some point, this is what we're planning for now:
Firearms
Firearms use explosive alchemicals to fire metal ammunition. Reloading involves drawing and tearing open a paper cartridge, which contains firedust and a bullet. The gunman pours firedust down the barrel, then packs in the bullet with a ramrod. Pistols and carbines are fairly easy to aim, but the extreme length of muskets (over five feet long) makes them unwieldy for untrained users.
Reloading takes a standard action. Normally powers that let you make multiple ranged attacks let you reload freely between attacks, but you cannot freely reload firearms in this way. For that reason, a typical character might carry a loaded firearm to use as a once-per-encounter weapon. A character who wants to use a firearm as a primary weapon should take the Firearm Expertise feat, which lets him reload as a minor action. A fully specialized gunman may also want Speed Loader, which turns it into a free action.
We understand that many gaming groups use Wizard of the Coast’s Character Builder, and that – barring revisions to the software – adding new items is impossible. For that reason, we have based each firearm on an existing crossbow. The firearms trade a slower reload time for the brutal 2 and high crit properties.
To give your character a firearm, just equip the analogous weapon. When you print out your character sheet, you just need to remember or mark the different traits. To give your character Firearm Expertise, instead take the feat Crossbow Expertise. You gain the same attack bonus benefit, but use the firearm feat’s faster reloading in place of the secondary benefit of the crossbow feat. Feats, abilities, and powers that apply to crossbows also apply to firearms, and any character proficient in a crossbow is proficient in the equivalent firearm.
We admit this is a bit of a kludge, but it should let you take advantage of the Character Builder’s automatic calculations of attacks and damage, while giving firearms their own unique identity.
Pistol. This weapon is analogous to a hand crossbow.
Carbine. This weapon is analogous to a crossbow.
Musket. This weapon is analogous to a superior crossbow, from the Adventurer’s Vault.