If you are going to use a macro like this, it is recommended to list the attacks in this order:

/ac "Heavy Shot" <t>
/ac "Misery's End" <t>
/ac "Bloodletter" <t>

By doing so, you can spam the button and will give priority to Heavy Shot and weaving your ME and BL procs in between your GCD. If Heavy Shot is listed last, you will delay setting off your GCD and if you spam quickly, you will sometimes not attack. I use this marco and have no issues with it.