Making double fire are attack.

So how would one go about doing a double firearm attack?

Could you elaborate on what you mean by "making a double firearm attack"? There's more than one way to read that.

When making a firearm attack with a double barreled weapon, you can instead take -2 to hit with two attacks instead of the one. You can do this both during a standard or full-attack.

When making a firearm attack with a double barreled weapon, you can instead take -2 to hit with two attacks instead of the one. You can do this both during a standard or full-attack.

Pretty sure its a -4 to fire both barrels, if thats what you're saying?

i.e. instead of rolling 1d20 you roll 1d20-4 twice.

I'm sorry, yes its -4 to each shot, that's what I get for not quoting the material. Link under Musket, double-barreled

Here's the relevant developer response: Link.

And yes, this is crazy-go-nuts if you have a spare hand and the GM allows enough free actions to reload both barrels 14 or 16 times to cover 4x2 iteratives, 3x2 Greater TWF, and 1x2 Rapid Shot. But legal, if your GM allows that many reload actions. Even I think that's a bit much.

You won't be seeing many double-barreled pistols of the infinite sky, methinks.

And yes, this is crazy-go-nuts if you have a spare hand and the GM allows enough free actions to reload both barrels 14 or 16 times to cover 4x2 iteratives, 3x2 Greater TWF, and 1x2 Rapid Shot. But legal, if your GM allows that many reload actions. Even I think that's a bit much.

You won't be seeing many double-barreled pistols of the infinite sky, methinks.

I'm not sure how that works now, since they nerfed weapon cords. How would he reload with no free hands (besides Synthesist)?

Hence the "spare hand". A Kasatha could do it rules-as-written. A two-level dip into alchemist can net a vestigial arm that can reload a gun, since it doesn't actually add more attacks than the character would normally qualify for, it simply allows the gunslinger to use that qualification. There are a few other ways.

Weapon cords were only half the problem, and nerfing them only affects gunslingers so long as they don't figure out other ways to get bullets back into their guns. Double-barreled firearms are a much bigger problem than TWF itself, as they grant a doubling of attacks no other feature in the game grants, and they do it for a class that already has top-tier damage, range, and accuracy.

Hence the "spare hand". A Kasatha could do it rules-as-written. A two-level dip into alchemist can net a vestigial arm that can reload a gun, since it doesn't actually add more attacks than the character would normally qualify for, it simply allows the gunslinger to use that qualification. There are a few other ways.

Weapon cords were only half the problem, and nerfing them only affects gunslingers so long as they don't figure out other ways to get bullets back into their guns. Double-barreled firearms are a much bigger problem than TWF itself, as they grant a doubling of attacks no other feature in the game grants, and they do it for a class that already has top-tier damage, range, and accuracy.

overlooked the "spare hand" part :)

Clarification on double-barrel weapons would be good. To me it seems gunslingers (at least musket masters) would be too weak with a single barrel weapon but are OP with double barrel.

It doesn't make sense to make them work like Manyshot (i.e. once per round) since one could easily quick draw multiple fully loaded DB pistols (or muskets) to nova. Imo it doesnt make sense to nerf free reloads either, since it should be easier to load two barrels at once than to reload one barrel twice: you can grab two cartridges at once, ram them down the barrel at the same time (get a double ramrod), etc. I would suggest giving firearms a damage boost and getting rid double barrel weapons, or only letting them fire one barrel at a time (in case you cant reload as a free yet, or ever depending on class/archetype).

Though I wouldnt say their range is top tier. A musket master with a Double Hackbut of Distance has 5 range increments of 100ft opposed to an archer with a non-magical comp longbow having 10 range increments of 110ft

And yes, this is crazy-go-nuts if you have a spare hand and the GM allows enough free actions to reload both barrels 14 or 16 times to cover 4x2 iteratives, 3x2 Greater TWF, and 1x2 Rapid Shot. But legal, if your GM allows that many reload actions. Even I think that's a bit much.

You won't be seeing many double-barreled pistols of the infinite sky, methinks.

Haha, I wrote up a build that used a double-barreled pistol, but never bothered trying to TWF with them. At at certain point you've just got enough damage. Invest in something tactical! At the very least double-barreled firearms can help free up the feat tax of playing a gunslinger.

Clarification on double-barrel weapons would be good. To me it seems gunslingers (at least musket masters) would be too weak with a single barrel weapon but are OP with double barrel.

Yeah, the question of how double-barreled firearms function really does justify an FAQ clarification. It comes up often and the rules have no direct parallel to any other option. Though my feeling is that if this were done, it would either be nerfed or it wouldn't be nerfed, we'd see a 1000 post discussion of the FAQ entry, and then it would be nerfed. So for now, maybe just enjoy it quietly. :)

On balancing the gunslinger, I'll resist the urge to go off-topic, but at least say that the issues go way beyond individual firearms. (In theory, anyway. I've never played as or with a gunslinger).

I argued vehemently against the limit-on-free-action FAQ back when it was a thing, and even I would have zero problem with a complete rewrite of double-barreled firearms to make them actually work.

The quick-draw several guns trick is neat for nova, but I don't think quick draw lets you holster them as a free action, so wouldn't you have to drop them? You'd be at least somewhat limited by how much you could afford to spend on extra guns. If you're looking to stat up Derringer Meryl with double-barrels, well, it'd be funny anyway. At high levels, you could probably afford it anyway.

I've never heard someone say that a single-barrel musket master didn't do enough damage. o_O At least, not once they hit 5th level.