Talk:41cm Triple Gun Mount Kai/@comment-24702213-20170529140417/@comment-5046483-20170530223935

^Ditto above. The Japanese had serious problems with not only the quality of their flashless powder because they used a large grain size, which often didn't fully combust in the barrel causing the shell to become slower and less accurate while also reducing the barrel life but they also had problems with their metallurgy. This was a side effect of Japans rapid modernisarion and industrialisation. They were stil getting to grips with techniques that were over a century old in Europe and the US.

On their larger guns (I believe it was mostly 41cm and the Yamato class guns, but it may have been the 35.6cm guns too) used a technique called wire wound construction which most other major naval nations had already phased out. While this type of construction did allow for greater resistance against internal pressure, it is believed that it also lead to excessive barrel droop (what do you expect, some of the British wire wound guns had 170 miles of wire wound around just one layer) and overall weaker barrel strength which would have excaccerbated the problem of lower muzzle velocity.

Finally, the US 16" guns on the Iowa while having a similar muzzle velocity of 762m/s vs the IJN 41cm 785 m/s, they had a much heavier shell at 1225kg vs 1025kg for the 41cm

TL;DR - Japan made bad guns, bad propellant and their shell weight was nearly 20% lighter than the US guns