Cannoneers, which is a Bangaa class, don't need an ability to use their weapons. Flintlocks, which is a Moogle class, must use the Prime ability before using anything else in their skillset. Both jobs can equip hand cannons without a support ability, though it is impossible to use their skills as another job. Are you sure that you have a hand cannon equipped? If not, make one at the Bazaar. There is a page on the FF wikia that shows all of the bazaar recipes.