Byakuya claims that mastering bankai takes at least ten years of training.
In the Bount Arc, Uryu has these issues with the artifact that he uses to fight without his powers. They have to learn how to summon their powers at will (with fairly amusing results at first, especially when Chad tries to remember what Ichigo's younger sister Karin looks like), although Orihime manages to improve to the point where she can use her Shun Shun Rikka without calling their names.
So trial and error wasn't a reliable method of figuring out what he could do or how, either.
He doesn't learn how to fire it at will until he reaches Bankai. Ichigo Kurosaki accidentally sets off his Getsuga Tenshou attack immediately following his achievement of Shikai.The BirdMen spend significant time learning the basics of how to fly, and for one particular character, it took a Die or Fly moment to learn it.
In fact, when the series was cut short at twelve volumes, Beet still arguably hadn't totally mastered any of his weapons! With foresight he learned to work around the axe's twelve-second materialization time, and over time got better at the sword bit by bit if nowhere near able to master it. He eventually learns to fire more than one shot with the gun, and comes closer to mastering the shield with training from its original owner (who was Not Quite Dead). Of course, he still had to learn how to use them, and after several years was only able to use one, the spear, effectively.