Thanks for looking that up for me. A difference of 100 lbs is a much more conventional figure, as I’ve found only a single reference implying that 20 lbs might be more accurate.
The British and Japanese guns are indeed the most powerful ship-mounted guns during the dreadnought period. To the best of my knowledge, the greatest range achieved with the 18in gun was 40,500 yards using supercharge propellants and increased gun elevation. The 46cm gun could reach to about 45,960 yards.
During the time when pre-dreadnoughts were gestating, there was an enthusiasm for so-called “monster guns.” You’ll find guns of up to 17.7in or so in various navies. These guns used shells that were light by later standards, and the muzzle velocities tended to be very low. Nevertheless, as a group, the monster guns were a flop with numerous barrel failures. The technology of barrel design was too primitive for the pressures involved, and the black powder propellant was little more than an explosive that threw the shell forward in one sudden heave.