The shells and propellant for the 16" guns are leftovers from World War II. The Navy had been operating a 27-battleship Navy during the War, so they had a huge quantity of supplies remaining after the battleship fleet was decommissioned.
When all four ships in the Iowa class were reactivated in the 1980s, the Navy calculated that the stockpiled supplies were enough to last for the remaining life of all four ships. It was this World War II-era propellant that ignited in 1989 and killed an entire turret crew on the USS Iowa.
The cause is believed to have been identified, and the Iowa-class battleships subsequently fired the 16" guns without incident. But that was back when the ammunition was 40-50 years old. Today, the ammunition is 70 years old!
Assuming you mean 16 feet (not inches), the barrel can be intact but that does not mean you have a working gun.
The firing mechanism on a gun that size is incredibly complicated and bulky, and would be easy to disable by removing, locking, and/or welding key parts.
