On page 98 of the TO:AR book, it lists the rules for rapid firing a standard/light autocannon. What it doesn't do is indicate what happens should you rapid fire said autocannon when using a munition type that also must resolve itself on the cluster table.
The question is: After rolling the cluster roll to determine number of rounds that hit, do you then roll cluster to determine how many fragments of each round connect. I would assume yes but official clarification is very helpful.