Ferocity Support Gem on Mercenary Bolt Skill Interaction

Was testing out Ferocity support gemon galvanic shards and it each bolt fired would consume a frenzy charge. Was hoping for the interaction to only consume a charge on reloading the whole clip and for the benefit to apply to the whole clip. Do you guys think this is the intended interaction or a bug from mercenary bolt skills being a "2 button" skill where you have to load and click crossbow shot to fire?