Modified for tinkers and bowyers:
Tools of the Trade
You possess a deep understanding of your art, which includes knowing how to most effectively use the weapons you craft.
Prereq: Craft(weaponsmithing, bowmaking, or clicker) 10, Area of Expertise(weaponsmithing, bowyer, firearms), Weapon Focus
Benefit: Select any type of weapon in which you have the weapon focus feat. While wielding a weapon of this type that you have crafted yourself, you may use the next best base attack bonus chart for the determining your BAB for the class levels that granted you the Area of Expertise prerequisite (crafter or tinker). For instance, a Fighter 4/Tinker 4 with this feat and 10 ranks in Craft(clicker), Area of Expertise(firearms), and Weapon Focus(firearms) would use the cleric chart for determining his BAB for his four tinker levels, and would therefore have a BAB of +7 when wielding a firearm or epbul he crafted himself. A Crafter 8 specializing in weaponsmithing would use the fighter chart for his crafter levels and would therefore have a BAB of +8 with a weapon he crafted himself.
Special: You may select this feat multiple times. Each time you do, it applies to a different weapon type. This feat may not be used to gain a BAB for the purpose of qualifying for feats or prestige classes.