Sometimes misfires from "11's are caused by the primer not fitting all the way down on the nipple. Certain brands of primers are (slightly) smaller than others and when the hammer falls, it merely "seats" the primer down on the nipple all the way. If the hammer is dropped again, it will usually fire. The problem is not that the primer is a dud, but it's not getting a solid whack when you pull the trigger the first time.
I had this with my ML with CCI primers and since I switched to Remington's have had no more problems. Some guys file their nipple smaller to accomodate the smaller primer, but it's easier to switch brands IMO. Sometimes all it takes is a more solid "push" with your thumb to fully seat the primer on the nipple.

Good Luck