Perplexing issue with a M1903

[Matt_G]

Long time lurker. First time posting here.
I have an issue with a 1903 that has me scratching my head.
Allow me to give some background, then the issue.

Background:
I have headspace gauges from PTG for .30-06. (Let's assume they are correct)
I also own a RCBS Precision Mic for .30-06.
The Go gauge I have measures perfect in the precision mic; it measures zero. (2.0487)
The No-Go gauge I have measures +.004 (2.0527) and the Field gauge measures +.009 (2.0577) in the precision mic.
This Springfield can close the bolt on the No-Go gauge but can't close the bolt on the Field gauge. Fine I think, it's a bit long but within SAAMI specs. It's between 2.0527 and 2.057

Issue:
I wanted to find out what the headspace was so I loaded 5 LC cases (FL sized) with Fed 210 primers and Hornady 3037 150gr. FMJ-BT bullets over 49.5 grs of IMR 4064.
Here's the perplexing part; I measured those 5 cases with my precision mic and get the following:
-.005
-.006
-.008
-.010
-.012


How in the hell does a chamber that measures at least 2.0527 put out fire-formed cases that are as short as 2.0367?
And why are they all over the place like that?
I have never seen this before.

Another thing, the primers were backed out significantly. The primer pockets on these case were not loose when I seated those primers, yet these things backed out at least .020 or more.

I am thinking I should throw this thing in the car and take it to Chuck Moline and let him look at it but I am curious if anyone here has any ideas as to WTH is going on.

Information

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[bml]

It is fine, common in milsurps. The firing pin jams the case forward. The case fires and expands. It grips the walls but there is not enough force to push the case head back to the bolt face. Instead the primer is pushed out to the bolt face.

I have a few 1903a3’s that do the same.

[Matt_G]

bml, thanks for that explanation.
I was not aware of that phenomenon, but the way you explained it makes perfect sense.

Steve762, I have to plead partially guilty as charged.
I do strip the bolt before using the gauge but I sure as heck wasn't using it as a "feeler gauge".
I will take your statement to heart in the future.