and what was your point? The ammo will return after a precision hit(so?), all that does is make it so you will be leaving a bunch of ammo on the arena floor. In PoE you'll generally have enough ammo to kill the boss once it shows up anyways.
PS if you're using your Primary to kill a boss in PoE you're just dumb. Use your special and heavy weapons when you can and the primary as the tickle distraction.