IDK if this is optimal but I use [bC] as much as possible and it is pretty effective to BR boost cancel 2 or 3 times then throw out [AB] just cuz, but IDK. XD
According to the wiki:
BR = 8 shots (75 damage)
[CSa] = 1.5 second charge (70 damage) *stops your motion (leaves you vulnerable) *good to boost cancel into melee
[AB] = 2 uses (25-150 damage on first use & 147 damage on second)
[AC] = 2 uses on full charge (296 damage) *also found that to hit on landing you should fire when they are about 1 suit height above the ground.
[bC] = 1 use (60 damage) *slow to recharge. *duration is 20 seconds or recharge is 20 seconds, wiki is hard to read
EX [ABC] = 1 use (356 - 350 damage)
Melee(s) = pretty fast & very good to boost cancel into melees when the opportunity arrives. *don't forget to combo using rainbow-step