Ok, when you say you "shot your first reloads" does that mean you did a ladder charge workup? Did an OCW workup? Could be your rifle doesn't like BLC2 under 75gr bullets. I've used IMR4064 under 68gr HPBTs and 2000-MR under 75gr HPBTs, but I have a 20" 1:7 twist.
Your primers should be fine, so try playing with the powder charge and seating depth to see if that helps.
Machine guns are awesome until you have to carry one.