Help me understand "Head Space"

What is confusing is the term "head" being part of "headspace". It's an historical artifact and is not literal in most cartridge designs now, except in rimfire cartridges. In a rimfire cartridge the rim is the pressure head (the barrier to pressurized gas escaping), so the front-to-back space the rim fits into in the closed chamber is literally the space for the pressure head, or headspace. The term simply got carried forward after cartridges with solid rims began to appear, and then was carried forward again when cartridges that didn't stop on their rims began to be designed in the late 19th century. At that point, in a relatively short time, we went from cartridges designed to stop against the rim to cartridges that stop against case shoulders, case mouths, or case belts, none of which are part of the head. But the distance from the breech to that stopping surface continued to be called headspace anyway, just out of habit or tradition.
Click to expand...

Just happened to re-read Unclenick's second part of his first post ( post #2 )

That's where all the confusion seems to come from and confirms my point that if enough people say something enough times . It will in fact become true .

I remember a thread here at TFL about a year or two ago that I finally told Guffey to stop arguing that there is only one place that head space is measured . I said enough people for a long enough time have used the term CASE head space in reference to the measurement of a case from the head to it's datum point . That it's now excepted as a valid term . If I recall he did not want to except that point of view .

So I propose we start calling excessive headspace , excessive head clearance so to be more accurate . Technically shouldn't the term excessive head space mean a chamber that was cut longer then max spec ? If we get enough people saying it and explaining why excessive head clearance is a more accurate term . The reloading world can have one less thing to debate .
 
Last edited:
Relax your mind, relax your mind. I do not care what you call it. If you can not measure it you are talking about it. I am surrounded by some of the most talented group of builders, reloaders, shooters. Not one of them acts in real life as bad as those claiming to be reloaders, shooters, builders on the Internet.

F. Guffey
 
Pretty long winded explanation, but it does point out that SAAMI gages are not EXACTLY compatible to MIL-spec or European spec chambers. I have never shot a 1917 Enfield, .303 Brit, or 30-40 Krag, ect. that was not hard on American civilian brass. If I remember correctly, most body diameters on the SAAMI spec case are about +.008. I have found Winchester brass to be on the low side out of the "Big three". It can look pretty ugly coming out of a 1917. On the other hand, military brass is a lot thicker and can cause issues in SAAMI spec rifles.
I have no idea why someone would experiment lengthening the front of a chamber. Putting a shorter cartridge in a longer chamber is a pretty common occurrence. I accidentally did it myself once. The wrong case assumed the dimensions of the chamber, including swelling tremendously right in front off the head. Just a guess, but I believe the brass outruns the bullet in instances like this. If the man wanted action, he should have increased the distance between the case head and bolt face and used a longer firing pin. Hey, wait a minute! Is that not the Original Poster's point?
 
You must log in or register to reply here.
Back
Top