Does anyone know how savage blow builds up now?

There has to be more to it than just early levels got raised to 4 hits instead of 2. Also, why at when savage blow was at level 10 it sometimes hit 4 times and at other times 5 (similarly, at level 13 it hit 5 and 6 times), has savage blow always had an ability like that? I'm rather new to making bandits but enjoying it as I make one.