Fixed ammunition was not the only 4.7-inch obstacle

Was fixed ammunition the main problem preventing a 4.7-inch dual-purpose gun?

Not by itself: the answer depends on the particular 4.7-inch weapon, and the chosen 45-calibre family already evolved toward cartridges but still needed better shell ballistics and funded development.

The phrase 'the 4.7-inch gun' covered several different weapons and ammunition arrangements. The Mark IX and XII lineage evolved from an earlier bag-propellant gun toward cartridge use, so fixed ammunition was not a universal disqualifier. Its existing shells were sometimes judged to have mediocre ballistic form, but the service accepted them as good enough while expecting the 4.5-inch programme to arrive. Redirected development money could have improved the shell, mounting, and high-angle system together.