After leaving the boathouse, Dillon fires the first gun he obtains without cocking it, meaning there was one round in the chamber. He is then unable to fire again because the magazine is empty. Why would a guard be on patrol with a completely empty magazine?
When Dillon is carried to the boathouse for execution his hand are tied behind his back but when he jumps in the water to escape suddenly his hands are tied in front of him. (Had his hands remain behind he couldn't have cut the tie.)