1.5" groups with the 350 grain FPB at 100 yards is fantastic. My Encore makes 2.5-3.0" 100 yard groups with that bullet. Not sure what happened to degrade your accuracy. Know several folks who use that bullet on hogs: They all say that loading technique can effect accuracy to a large degree.
Insert the bullet in the QLA then give the quick starter a very hard rap with the heel of your hand to get the bullet into the rifling.