If you carefully file any crater flush with the primer, and hold the case, lengthwise, betweeen the jaws of dial or digital calipers, holding it up so that the head of the case is between your eye and a light source, what do you see? Is the primer protruding? If it is, record the length of the case including the protrusion, knock out the primer, with a punch, and remeasure the length of the case.
The difference will be the protrusion. Add to that the fact that new cases take several firings to reach their maximum datum line to head length and you may have solved your problem. That old Springfield has a heavy firing pin and the case design lends itself to the case being driven forward in the chamber. If you want to get a better Idea of what your chamber looks like, work up a load that is hot enough to leave the primer flush after firing, but is still by the book safe and then fire the same case several times while only neck sizing using something like a Lee Loader to size, so that there is no potential for distortion by dragging an expander ball back through the neck. Here is a post that I wrote on another board about a middle of the book 150 gr. '06 load in a Springfield with a new military barrel.
I was going to address this in a later post but to your point of how much pressure it takes to stretch brass to the bolt face, let me give you the following example.
"Many years ago I had a Springfield that had a newly installed Smith Corona 03A3 barrel. One day I decided to do a little experiment. I went to the range with all the necessary tools to reload 30-06 with a Lee Loader (neck sizes only, no expander), including an old Hollywood micrometer type powder measure for which I had made a setting table for AA2520. I decided to work with some 150 grain bullets that I had at the time, and noted the loads for that weight from a manual, deciding to start with a middle of the book load.
It is at this point that I should mention that the barrel interior was a bit on the rough side, but with no function problems. I think that the chamber must have been as reamed (no polishing) and it may have been that the bore was not plugged when the Parkerizing was done.
In any case, I made up some loads at home, perhaps half a dozen, and when I shot them, I noticed that the primers were slightly protruding. Curious, I reloaded and fired the brass several more times with the same load. Each time the brass came out with the primer backed a little farther out of the case. The last time, even though the brass OAL was correct, the shoulder had been moved so far back on the case that the neck was starting to be reduced in diameter at its end by the angle at the end of the neck portion of the chamber. After that, being young and impetuous, I decided to risk a full pressure load, and after that the cases came out with the primers flush and a bright line just above the case heads, denoting the presence of what is called an incipient separation. At that point I flattened the necks to prevent the reuse of the cases, and threw the cases in the trash.
This is what had happened. The Springfield has a very heavy striker assembly, and that particular one had been fitted with the heaviest spring that strong hands could manhandle onto it. The '06 has a relatively small shoulder angle, and the heavy whack from the weighty pin was driving it forward in the chamber. At that point the pressure generated by the burning powder became great enough so that it was held in the forward position, so that the only way that the head could have come back to the bolt face would have been for the brass to stretch just in front of the head, which in the case of the first firings, did not happen.
Now to your point. Middle of the book, jacketed bullet loads' pressures are not miniscule by any means, yet in this case they were insufficient to stretch the case back to the bolt face. "
