Can someone do me a favor and mic a FIRED case at the case head? Please use something that is accurate to the third decimal.
SAAMI calls for .376, my dies push mine back to .375-The reason is below:
I shot my STG556 this weekend, and it ran flawlessly. Awesomely quick on target and very low recoil and fast follow up. I picked all my brass and took them home to resize, and promptly got 2 cases stuck in the dies, even with copious amounts of lee lube. I could not figure out why there were so difficult to resize until I ran my micrometer over them and found the case heads were .380, and behind the shoulder was .363.
So I measured brass fired from another NATO chambered rifle of mine and got case heads of .378 and behind the shoulder diameter of .359
This tells me that the chamber in my STG556 is possibly a bit on the large side. I have emailed Dave, who has already offered to check everything out for me (Thanks Dave, you rock dude.) but I don't want to waste his time and money if this is a normal thing. This is not a max load, Lake City brass, 26 gr of W748, COAL of 2.23, Hornady 55gr FMJ, slight crimp in the cannulure. Primers were fine, and there were no pressure signs. I never load max loads anyway, as it saves my brass.
The downside is that I will only get a few loading from each case as they work harden from being sized a lot, and it may cause me to drop a testicle when resizing.
My Stag AR keeps all the cases with the same load at .377-.378, and these resize with very little effort, and usually do not require trimming until fired at least 3 times. All the STG brass had lots of trimming after resizing from only one firing.
Thanks in advance.

Things I have already checked-
Dies and cases are clean and cases are well lubed before sizing.
Visual inspection of the STG chamber shows no visible defects, I do not have anything to measure chamber dimensions.
Ejection was brisk and consistent at my 4 to 5 o clock at about 10 feet on normal gas setting.
The STG is light years ahead of my AR as far as point shooting. :)

Thanks Dave. You are 90% of why I brought this weapon. I almost want to give you my firstborn, but since she is 19 now, she may have an issue with that.

I used to build really large steel ocean and brown water barges. I am in nursing school now.
I will send out my barrel tomorrow. Thanks Dave.

I sent the barrel today Dave. My Fathers funeral had me busy the last few days. I put in some cash for you to get a coke and a hamburger(or your choice of some kind of fast food)
Thanks.