This shell was not found in seawater, so I do not know if salt is the source of the problem. By the way, I'm not a shell collector. This shell is the only one I ever bought, because it is so important historically. It is very,very seldom in warfare, that a munition wins a war. Most people in the world have been made to believe that the Atomic bomb won the 2. World War. But that is not the case. Incendiary bombs destroyed many more citys and the storages were overflowing in 1945 while production was at its height. For those who are interested I can recommend very much the extremely well researched work "Making Goop out of Lemons", which you find online. The above pictured Prussian shell won the Prussian-Danish war. Or better said, it's fuze. Up till that time all explosive (Black Powder) bursting shells had a time-fuze. All the danish shells, all spericals, were mostly fuzed with wooden time-fuzes. The prussian fuze "Zuendvorrichtung (aelt/C)" was the first mechanical impact fuze, just newly introduced in Prussia. Thus the prussian artillery was able to let their shells explode in the middle of the defenders at the "Dueppeler Schanzen", while the danish shells exploded before , behind or too high, with little effect. I attach a drawing of this first prussian fuze.
regards,
Bellifortis.