Although you are not a gunner, you have and can use grit.
Prerequisite(s): You have no levels in a class that has the grit class feature.
You gain a small amount of grit and the ability to perform a single 1st-level deed only from the base gunner’s deed class feature, using the deed as if they were a 1st-level gunner. At the start of the day, you gain 1 grit point, though throughout the day you can gain grit points up to a maximum of your Wisdom modifier (minimum 1). You can regain grit using the rules for the gunner’s grit class feature. You can spend this grit to perform the 1st-level deed you chose upon taking this feat, and any other deed you have gained through feats or magic items.
Special: If you gain levels in a class that grants the grit class feature, you can immediately trade this feat for the Extra Grit feat.