Gunsmithing says:
Benefit: If you have access to a gunsmith’s kit, you can create and restore firearms, craft bullets, and mix black powder for all types of firearms. You do not need to make a Craft check to create firearms and ammunition or to restore firearms.
Do does this mean you just grab/buy some metal, wood, oil, gunpowder, and lead; and several 8 hour rotations later per 1000 GP of 1/2 the market value of the firearm (less for the ammo)……Presto! Here's your gun. No need for Craft: Gun-smithing or any ranks in the skill?
Best Answer
Yes
The feat removes the need of using the Craft skill to make guns or ammunition.
The availability of the feat (and firearms in general) is entirely up to the GM. In a setting where firearms exist but are rare, the feat might not be available. As such, anyone interested on making guns or ammo must use the old fashioned way, the Craft skill.
In another setting firearms are common, people who are gunslingers have enough knowledge (and technology) to be able to make their own guns and gunpowder much easier and just spend enough money and time, no special skill required.
For alchemical ammunition, you require at least 1 rank in Craft (alchemy), as explained on the feat:
Anyway, the point is that the availability of each of the firearms mechanics depends on how rare the GM wants firearms to be. This is explained in the Ultimate Combat under the firearms rules:
Keep in mind that a gunsmithing kit provides all tools necessary for the job, and is required regardless of the rarity level.