Define bigger gun. Up to 57mm? Up to 76mm? Up to 127mm? The point is the new gun, whatever the size, will be to replace the capability currently provided by the Armidales. The gun won't be for NGS, it won't be for ASuW, it will be to do the same thing the current 25mm gun does, only do it better.That's cool, next time I'm having a chat with one of the bid or project directors I'll tell them they were wrong when they told me the RAN were looking at a bigger gun than the 25mm Bushmaster on a Typhoon mount.
Volk, I think you are deliberately concentrating on specifics at the expense of the greater point - Navy are buying a capability to replace the patrol boats, not a small surface combatant. People who are expecting the OPVs to be >2000 tonnes, with CIWS, SAMs, medium guns etc are going to be disappointed.