GT,
What did you mean by "new" neck-sized? Fired once and neck sized for the first time, or new cases not yet fire-formed, but put through neck sizing? The latter could slide further forward than the COL would normally indicate if they are shorter than book.
What is the rifle? Normally, unless it is a revolver (in which case, yikes!), bullets tend to be pushed into the case by recoil banging the front of the magazine into them, or against the next bullet in the case of the tubular Mag. Pulling definitely suggests a long seating job sticking in the throat, so I would check the case sizing as in my last paragraph. Worst case, you may want a chamber cast to compare to your loaded round.
Has he experienced the problem with factory ammo? If not, I would closely compare the ones you assemble to one of those with a bullet comparator.