The min spec neck is what I am thinking right now. I will recheck the gauges but I had a friend with me when I tested it. I am measuring the cases NOW. Length of fired case 2.532.5. Unfired case 2.529.5. Lyman 49th max is 2.540. Shoulder is 1.948 on both the factory ammo and the fired case. The rim dimensions are .4515 for for the unfired and .4516 for the fired cases. Just ahead of the rim on the body the unfired case is .4114 and fired case is .4115 with multiple measurements with a mic. Shoulder mics out at .4215 on the factory case and .4217 on the fired case. The cases measured are R-P head stamp.
The primers are not abnormal to my eye; poor that they may be. They measure out within .0095 below the head for the factory ammo and .007 on the fired case. There are no marks on the case heads.
These are multiple measurements and appear to be within specs. I realize that there is spring back of the case on firing. I rechecked the chamber with the no go gauge and it chambered. I do not have any unsized cases from the Mossberg. I do have some cerro and will do a chamber cast when it cools down and I have the time as I am nosing around for a new job.
Everything contradicts and I am puzzled. I will check with the fellows on Grey Beard. Nothing makes sense at this time. The brass seems to be within specs. The rifle locks up well and does not flop open on shooting.