Wait for at least one of his claws to open then start shooting them. Do not lock-on because they will probably hit a different part of his body. Once he screams "No!" and flies into the air, you must destroy all his legs and his claws. Locking-on can be done, but it is not recommended. When all his legs and claws are gone, his mouth will open. Shoot it until he dies. Note: Shooting the eyes can also be done because he attacks with them, but they will return after awhile.