There is actually no comparison between even the 13.5" Queen Mary and 14" KGV gun. The 14" gun has 25% more armor penetration at 10,000 yards, and 90% of the 13.5" gun's 10,000 yard penetration at 20K. Interesting, the 15"/42 on the Queen Elizabeth/Hood had only a 5.7% advantage over the later...