How big is that gun, anyway?
I don't suppose there's any chance it could be 155mm and use the same wide range of ammunition types that all the NATO armies have available? And all the R&D paid for by someone else, too.
It's funny that you say that as a navalised 155mm gun is being talked about.
Royal Navy Prepares to Roll out the Big Guns
The proposal was/is for 155mm guns for all frigates and destroyers.
This
article by Tony Williams may be of interest:
More recently BAE Systems have changed tack and are now offering a new concept, the existing 4.5 inch Mk 8 naval mounting with the gun switched to the 155mm L/39 from the AS90 (surplus barrels being available). This is known as the 155 TMF (Third generation Maritime Fire support). The existing mounting is apparently strong enough to stand the additional weight and recoil (and could also accept the 155mm L/52 if required). The weight of the 155 TMF mounting goes up from 22.5 tons (Mk 8 Mod 1) to 24.5 tons. although this is still lighter than the original 4.5 inch Mark 8 Mod 0 at 26.4 tons. Other modifications needed to the mounting include a double-stroke loading cycle to fire the separated ammunition (which would presumably halve the RoF to around 12 rpm) plus some adjustments to accommodate the wider ammunition. It appears that the gun will use a single-module L10 artillery charge. Obvious advantages include commonality of gun and ammunition with the British Army (with a huge long-term saving in future ammunition development costs), 80% commonality with the existing Mk 8 Mod 1 mounting without requiring the "navalisation" of an army turret, and greater destructive power than the 5 inch gun with a longer range than even the new 4.5 inch Extended Range ammunition: 30 v. 27 km. There is clearly the potential for far greater range and effectiveness increases in the future using advanced ammunition, including guided projectiles; for instance, Italy is planning a 155mm artillery version of the 5 inch Vulcano ammunition (see above). The RN is very keen on the 155 TMF project, resulting in the award of government development funding in 2007. The main problem to be solved is the handling of the propellant charges, which the RN requires to be encased for fire safety reasons.