In my third to last Greyhawk campaign, there were some significant naval battles in Year Two.  Unable to imagine naval warfare without cannons thundering off the broadsides, I was glad I had decided before the campaign that gunpowder would work on my world of Greyhawk.  The players were informed that rifles and pistols also existed, but had never come into common usage.  The players' actions reflected that; in 10 years, not one of them ever chose to use a rifle or pistol in lieu of more traditional weapons.

~Scott C.

I was reading the Grimms' tale "The Expert Huntsman" and it brought to mind whether anyone had ever included something like an air-gun in a D&D campaign?

I can easily picture an adventurer with something like this:

complete with a dedicated hireling or two to team the wagon pump.

I read a short article in an old S&T (when it was by SPI) about an experimental airgun in the Napoleonic era.  Lethality was nearly on par with muskets of the time for the first dozen shots or so and it wasn't much bulkier.  It failed to be adopted because of expense, required additional training, and it was more fragile in field conditions compared to a musket.  
 
In a Napoleonic spy game, a gun that fires multiple shots with little noise or smoke would be a cool toy.

Quote from: Nicephorus;416075In a Napoleonic spy game, a gun that fires multiple shots with little noise or smoke would be a cool toy.

I've wanted to try running D&D against a more 1700s/early 1800s backdrop for a while.

Quote from: RPGPundit;411727Incidentally, what kind of level of frequency do you like having these weapons in your games? Personally, I like for them to be quite expensive and only available for purchase in metropolises. RPGPundit

The catalyst in my game is created via alchemy and magical enchantment. With firearms being a rather recent introduction to the world. With the combination of deep professional and personal arcane talent serving as the requirements to craft "blast (/thunder) powder", its not only hard to locate with any regularity, but its very expensive to boot. Add to this that the firearms themselves require regular maintenance in order to function properly, but because of their "young" nature are less reliable than your crossbow. The upside being that when functioning at full potential, thump (/boom) canons can be extremely lethal when compared to more established weaponry. Save for other high maintenance weapons like an engineered chain sword or repeating crossbow.