When I’m seating bullets into new (unfired) factory-annealed .308 Win Lapua brass cases, for years I’ve noticed that, when seating the bullet (via a RCBS RockChucker single stage press using Redding Competition dies), approximately ~ 1 to 2 out of 20 (i.e. 5-10%) of all cases produce significantly reduced neck tension during the bullet seating process.  The difference is a factor of several fold.  Question: I haven’t isolated and chronographed those low-neck tension rounds.  Should I?  I realize that for the Sierra 175 grain Tipped Matchking bullet fired at 2,620 fps MV, a mere 20 fps MV deviation results in a significant difference in drop at 1,000 yards.

I have experienced that as well. I usually set those aside for fouling shots.

It's even more noticeable if you measure seated bullets. I use a Redding instant indicator die.

Ive noticed that most bullets are within 1-2 thou of each other when seated, but those light neck tension rounds tend to be vastly different, up to 6-7 thou deeper than the rest (less resistance).

I definitely sort them out.

The minority to which I'm referring (5-10% of these Lapua cases) are super light on neck tension.  I also resize neck only via Redding sizer ball before seating.

OP, I have ran into that on normal bass, annealing the harder to seat brass twice brought them back to close to each other..