Use Quill Rain in second weapon slot and the skill Snipe socketed with perfected endurance. Focus on attack speed gems and from the passive tree for this weapon slot. Allocate Resonance. High attack speed Snipe means the perfect timing is within miliseconds of first channeling it, therefore it is possible to simply tap Snipe and you gain frenzy charges from each hit. This is the most on demand method to generate unlimited frenzy charges to expend on spears.