You didn't say Which brand got the FTE on trips 2 and 3? Remington? WWB?, or Federal? Federal is a common variable in all 3 trips (not used in trip one, where you had 0 problems, but used in trips 2 and 3)
... but USUALLY, Federal is considered a very reliable brand.

Could be ammo related, could be something else.
Take variables out of the equation to be sure.