It's really your choice. As a combat round is a flexible amount of time, you can choose whichever way makes sense.

If they are the primary weapon of the setting, Prepare, Slow-firing and/or Limited Ammo might get tedious.

However, if ammo is scarce, that alone could have an impact as reloads cost money.

It really depends: do you want your players to have to spend manoeuvres to reload? If that's the feel you're going for then yes, they should! But if you don't want to have them worry about silly things like reloading (I mean, they have 6 pistols at their belt, right?) then don't.

The fiction informs the rules, not the other way around.

Early firearms are unable do to Autofire, even if there's more than one barrel on the gun. It's only around the years 1820-30 that the technologies for repeating gun was found. One gun can only shot one time and then must be reloaded before being able to fire again. One manoeuvre to reload one gun but with the option of Talents to reload the same gun more than once per round without having to spend another manoeuvre.

You must add the possibility of misfire each time a gun is used. That was the scourge of early guns, they were totally useless in wet weather. Another problem was they sometimes exploded in the face of its user. For misfire 3 threats seems right and a despair to cause explosion the gun. That'll do for very early guns form 15th to 16th century, but not for less early guns from 17th to early 19th century. For those the risk of explosion mostly disappeared and misfire became a lot more rare, mostly because the way guns were fired was a lot more secure and more isolated from the ambient humidity level.

16 hours ago, WolfRider said:

You must add the possibility of misfire each time a gun is used.

He really doesn't "must" add it. There is no requirement that these games are 100% realistic, quite the opposite. Sure having that as a feature if enough threat/despair is rolled, would be thematic, but the OP can ignore it if they want for their setting.

OT:

On 10/28/2019 at 3:17 PM, SiraoGomes said:

Pretty much just the title. Brainstorming a setting where early firearms are fairly prevalent.

Bold for emphasis. Since you described it as this, that would imply they are at a level of being commonly available, which would imply they've reached the point of reasonable level of mass production. Which could easily imply they've reached the point where they fire reliably, and also fire quickly. If we're talking muskets then yeah I would say they are slow, but it's not that big of a stretch to let them have revolvers, or bolt action rifles, which can be fired pretty darn fast, excluding the need for the Slow Fire trait.

Really it depends on what you and your players want. Do you want constant bullets flying every turn of every fight, because everybody is sporting a gun, and they fire quickly enough to make it all just gunplay? Or do you want the option for guns, but have them be sporadically used in combat, perhaps every other turn, allowing for the people to potentially charge in for melee while someone is reloading, or swing from a ship to another ship inbetween volleys of fire?

Depending on which way you answer those 2 questions, that should give you an idea of how you should handle the weapons.

Personally, I like the idea of having them be Slow Fire, if only because it makes for more opportunity for fun situations, where the people have to come up with something else to do, because they missed their shot, and they don't have time to stop and reload it while in a fight. Perhaps they do a running/reload action for a turn or two, all the while engaging in banter with the enemy. Or perhaps they try and set up some kind of thing to fall on the enemy, while they are busy standing there reloading, taking advantage in the lull in bullet fire.

In the end though, it should be something you just ask your players. Give them your thoughts on the pros/cons you see for either method, and ask them how they would like to handle it. Then go with that.