Bart B. I do not “...must know...”. There are two specs for the 223 Remington, Sammy and Government/NATO, there are two specs for the 308 Winchester, Sammy and government/NATO. I do not wonder why that is, there is the public sector, there the government/military/NATO sector. When Sammy decides to include the 50 BMG into the public sector there will be “SAMMY SAYS” and there will be what the government/military/NATO says.
Then there is ‘always’ the question” What is the difference between 5.56 NATO and 223 Remington?
Gages existed before Sammy, I have had old 30/06 gages that did not agree with Sammy type gages, for me, nothing changed, I measured the length of the chamber, I measured the length of the case from the usual places, I subtracted the difference, the difference was in thousandths, this method meant nothing to no one else but for me I knew the effect the chamber would have on the case before pulling the trigger. And firing pins, my firing pins are mechanical driven, my favorite firing pins hit like a go-rillo.
I know what Sammy says, I know what the government/NATO says, they do not agree, me? nothing changes, I determine the length of the chamber from the bolt face to the shoulder of the chamber, I determine the length of the case from the head of the case to the shoulder of the case.
Old gages, some required the extractor to be removed.