There seems to be varied information about how to use these though. Are you able to explain how you use it, without going into the specifics of jet sizes? In particular, how many detonations per km is a standard accepted number? I've heard HRC figures of 10 per km...
Anyway, if A is the largest I take it that C is the smallest? It seems logical, but with NSR pistons and barrels it's not always so...