(aka "case headspace").
...and room in a chamber for a cartridge case. That's the proper meaning to my mind, which is why I put the aka in parentheses. Back when all centerfire metallic cartridges had rims, "rim" was synonymous with "head," a pressure head being defined as the end cap that closes the end of a pressure cylinder. The sides of the case were considered the cylinder. So, at that point in time, headspace was literally the amount of space cut into the chamber for the rim/head to fit into, and head clearance was any excess space there was for the rim inside that headspace. When Mausers and other rimless cartridges came out, they just kept the term "headspace" for the room in the chamber for whatever surface the cartridge case stopped against when you dropped into the chamber, even though shoulder space or case space would have been more descriptive. In light of that, the reason "case headspace" makes no literal sense is that you don't qualify or disqualify a cartridge case based on how much room it has inside for another cartridge's head—or any other part of another cartridge. It doesn't need space for a head. But applying the term "headspace" to cartridge cases seems to be sticking for a lot of people, even though it appears to have come about from a misunderstanding that measuring a fired case from head to shoulder datum was an indirect or transfer measurement of the headspace of the chamber that fired it, and thus the gauge that measured the case serving as the transfer was a "headspace" gauge. You can see how that might get twisted up to be thought to be referring to the case itself. Especially when folks measured after resizing, at which point there was no longer any dimension transfer going on.Marco Califo said:I thought headspace was room on a boat for a toilet.