OTL?
LNT "Cruisers, Surface vessels of war, other than capital ships or aircraft carriers, the standard displacement of which exceeds 1,850 tons (1,880 metric tons), or with a gun above 5.1 inch (130 mm) calibre."
6"/50 (15.2 cm) QF Mark N5 and 6"/47DP (15.2 cm) Mark 16 would strongly disagree.......
Thanks for that. Knew I missed something, but it doesn't affect the upper range, it seems.
Any good 6" AA gun would have to be some manner of autoloading and would have to have an incredibly beefy mount, as the range benefits given by the larger shell don't really pan out unless AA is comparable. The US did try to start work on the 6"/47 DP gun OTL, but it ran into the age old issue of having no dedicated platform and constant halts to the design. If you had steady, consistent and dedicated development during the 30s, I could see a DP gun by the 40s, but its efficacy would be up in the air. The Mk 16 had inferior autoloading compared to the 8"/55 RF, which did have some potential to be redesigned into a new 6" DP gun, but the wars ended before it could see fruition.
I will note that the 5"/54 had a noticeably lower RoF than advertised as the heavy weight of the gun shells tired out the crews quickly. A heavy 6" shell would tire out gun crews even faster.