Heavier Nelson shells would require a deliberate gun rework

Could Nelson and Rodney use a heavier, lower-velocity 16-inch shell, or would that require new breech machinery?

It would require some gun work and investment, but a wider 16-inch program could make the conversion practical.

The Nelson-class 16-inch guns could be adapted for a heavier, lower-velocity shell, although the change would require engineering work and investment. It would involve more than issuing new ammunition because the gun and its loading arrangements would need reconsideration. A later British decision to arm the King George V class with 16-inch weapons could justify that expenditure. The same program could then modernize Nelson and Rodney rather than leaving their original guns as an isolated system.