My big gun designs

I was looking at my papers from my ship building program/planning game from 30-some years ago. I noticed a page with gun data. My 15-inch gun was pretty standard: 42 calibers and a weight of 97 tons. My 18-inch gun was 45 calibers and had a weight of 179.5 tons. The muzzle velocity was 2,800 feet/second and the AP shot was 3,645 lbs. The muzzle energy was 198,027 ft-tons. I don't really know how to use muzzle energy, but old Jane's Fighting Ships would generally supply this figure.