Looks like the bullet on the right has been shoved into the lands and has been set back. Hard to tell with picture clarity but it looks like that bullet has rifling grooves in it. Pull the bullet, empty the powder and see if the brass will chamber without the bullet. If it chambers ok, at least you can eliminate that. It's hard to imagine a barrel with a bad throat getting through the proof testing portion of QC, but I guess stranger things have happened.