that is because you do not understand what “caliber” means. a “five inch/38” means the bore is 5 inches and the barrel is 38 bore diameters in length. a 127/54 means the bore is 127 mm and the barrel is 127 mm time 54 mm long. the 127/62 is just using a bit longer barrel.
I was along as crew chief flying fire control at about 5,000 feet for the New Jersey in ‘Nam 1968....NJ was sitting about 3 miles offshore, the 16” guns made blast ripples all the way to shore, and the shell in flight was clearly visible with the naked eye...big BOOM at the end of the trajectory, too. Awesome!