Something definitely seems wrong with the rate of arcane missile generation. I can go entire fights without seeing a single proc, and considering it's kind of half my damage it feels kind of broken.
fwiw; i actually sat down and cast 100 arcane blasts at a training dummy and got 32 AM procs
it could be that the calculation is 15% base x 2 for AB + 3% for the artifact power, which works out at 33% in which case it's generating at the rate it's supposed to
if blizzard's intention was for it to be (15% base + 3% for the artifact power) x 2 for AB then i don't know how statistically unlikely it is to get 32/100 for something that has a 39/100 chance but my guess is it's not overwhelmingly unlikely
the problem is, i think, the proc is unlikely
enough that it's not unusual to go through an entire mana bar for a burst phase and see only 1 or 2 AM procs, which, with how expensive AB is and how little bonus mastery gives, puts a pretty serious cap on the amount of damage you can burst out while emptying your entire bar.
[edit] for instance, i just tried a basic burn phase on the training dummy, starting AP and throwing out ABs until i was out of mana; 15 ABs, 3 AMs, which is barely enough regen for one bonus AB.
