This isn't my first day at the rodeo, I've been handloading since the mid '80's (don't let my profile age fool you - I never entered it and don't know how to change it). I use a bullet comparator but not a cartridge one. I can solve that.
Turns out that the barrel is goofed up from Savage. Upon inspection with a bore cam, it appears that a chip found its way onto the reamer flute and damaged the neck/shoulder junction. Somehow this was missed in their QC check - imagine that! No worries, I have a 6 CM reamer and will need a 6.5 pilot for it. I also have 6.5 neck and 6.5 throat reamers. I'll take .100" off the breech then deepen the chamber and try this barrel again.

I suspected an out of spec FL die and I will check that too - Thanx SharpShooter

Load was 42 grs of Big Game and a 120gr Sierra Game King in Nosler brass with a Fed primer. It was my starting load. The first 3 look normal, #4 had a ring on the bottom and #5 came apart.