Hello,
I can offer some clarification to some of the terms used here.
- 'Salve Utili' is 'Effective' or 'Useful' Salvoes - the % figure refers to the percent of salvos in the shoot with a dispersion of 1% or less of the range.
- 'Colpi sul Bersaglio', as already noted here, is rounds on target.
- 'Ritmo Medio' is the average rate of fire of the shoot, or, rather, the average firing cycle.
- 'Colpi Anomali' or 'irregular/abnormal shots' is actually not clearly defined by any of the books I have, so I can't do much more than speculate, but it seems to be irregular rounds in terms of dispersion/fall of shot.
- 'Colpi Perduti' is 'lost/failed rounds' - this refers to rounds that failed to fire for one reason or another. Which was a considerable issue during the early work-up and calibration of both gun systems, as seen in the table above, though much less of an issue by 1940.
- 'Dispersione Longitudinale' is 'Longitudinal Dispersion'. This is taking the average fall of shells away from the MPI (mean point of impact) of a salvo and doubling it, which gives you your average salvo dispersion in range.
- 'Apertura Longitudinale' is 'Longitudinal Spread'. This one is a term who's exact significance is somewhat unclear with me. The definition given is, as DrG indicated above, the distance measured between the shortest and longest shots of a salvo. This would tend to make one think of a discussion of the maximum spread seen in any salvo of the shoot.
It is worth noting, however, that in the English-language version of Bagnasco & de Toro's book on the
Conte di Cavour and
Duilio-classes, they include a note that does not exist in the Italian monographs with the same table, which states;
"Note: In these tables 'spread' relates to the opening salvo, while 'dispersion' covers the following salvoes." In light of that, I suspect that 'apertura longitudinale' is referring to the maximum spread of the opening salvo, while 'dispersione longitudinale' then covers the average dispersion of the salvoes in the rest of the shoot.
This, to use this as an example;
Thus, in this 320mm gun test, the shells landed in a roughly 700 meter diameter circle with 2.6% hits. That's about a 1% chance of hitting a nonmoving destroyer, 2.6% on a light cruiser, and 4.7% on a battleship.
One could fully describe this as;
"In the 320mm gunnery exercise carried out at 1st charge and a range of 23,600 meters, 44% of salvoes had a spread of ≤1% of the range, and average firing cycle was 48 seconds (1.25 rpm). 12% of shots failed to fire, while 4.5% of shells behaved irregularly. Spread of the opening salvo was 769 meters in range, while average dispersion for the exercise was 620 meters. Overall hit rate against the target was 2.6%."
*edit - apologies, realized I was missing a rather important 'not' in the comment on the term 'colpi anomali'