There is a whole study that compares the best WW2 Battleships against each other. Some interesting reading. You can find it here:
http://www.combinedfleet.com/baddest.htmBelow is an Excerpt from the report talking about the Main Battery Guns:
GENERAL COMMENTS: The Japanese 18.1"/45 reigned supreme as the most destructive piece of naval ordnance ever mounted afloat. However, its ballistic performance was not particularly inspiring, and the performance of its Type 91 shells was inferior to the norm, partly because they were optimized for underwater trajectories 7. Immediately below it in terms of power is the US 16"/50. Good ballistics, and superb shells, give this gun a tremendous whallop, and in combat terms I rate it as the equal of the Japanese weapon, largely because of its shells. Below that, in an upset, comes Richelieu's 15"/45, as the best all-around 15" gun, and feel the most useful in an actual combat situation. The Italian 15"/50 was an enormously potent weapon from a raw power perspective, but it sacrificed a lot in order to achieve that performance, and had decidedly inferior shells. I should note, though, that I am still investigating this particular gun and her shells in more detail; the information available on her shells is rather spotty. Bismarck's 15"/47 shell is 10% lighter than the French and Italian, although her cyclic rate is attractive, and her guns were very accurate. At the bottom of the spectrum, King George V's 14" gun clearly doesn't have nearly the oomph necessary to compete with the rest of these guys.
