Once you get Grav.round you should NEVER ever think of using charged bolt, just remove it from your bar. Unless ofc. you are some perverted gunnery/assault spec w/o grav.round meaning you are doing it wrong anyway
Staying at 90-100% is a waste of potential procs from FA. Ammo regen is maxed from 61-100% ammo, so you should ideally stay ~70%
Speaking only for gunnery since i have not much exp as Assault spec.
The best rotation rather there is priority. Depending on the situation - solo, group, PvP, PVE. providing there is a tank and you are not getting hit (this ***** the FA dmg due to the lame game design atm) your best skill is FA, followed by HIB and DR (with 5 vortex stats) and grav.round. Just rotate them at your own discression.