I think the above posters are right, although I haven't tested this for myself.
But from a
thread from the O boards I've had bookmarked for a while, I read the following:
Shortshot wrote:
since im a cheap *******... I combinded this macro with another
#showtooltip Steady Shot
/equip Sharp Arrow
/castsequence Steady Shot(Rank 1), Auto Shot
/equip Blackflight Arrow
it actually works... I love it :)
And although I have a limited knowledge of macros, I think the above macro would equip sharp arrows for steady shot (which is not affected by arrow damage), and equips blackflight arrows for auto shots. Not sure exactly how or why though :P Hope this helps.