Seriously I would give Winchester a call and see it there was a problem with that lot of ammo.
But out of curiosity and it may sound dumb, but did you try any other ammo? I can tell by your posts that you do reload. But the last time you fired your rifle did you pick up the spent brass? Maybe you shot at an animal and forgot or lost the spent casing. I could be that the case ruptured and there is a small piece lodged in the chamber. Seems very remote. But stranger things have happened.