Thread: Headspace
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Old December 29, 2018, 11:26 AM   #11
Jim Watson
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Join Date: October 25, 2001
Location: Alabama
Posts: 15,353
The current terms and definitions according to SAAMI are:

HEAD CLEARANCE
The distance between the head of a fully seated cartridge or shell and the face of the breech bolt when the action is in the closed position. Commonly confused with headspace.

HEADSPACE
The distance from the face of the closed breech of a firearm to the surface in the chamber on which the cartridge case seats. 1. BELT: A type of chamber design in which the cartridge seats in the chamber on an enlarged band ahead of the extractor groove of the cartridge body. 2. MOUTH: A type of chamber design in which the cartridge seats in the chamber on the mouth of the cartridge case. 3. RIMLESS: A type of chamber design in which the cartridge seats in the chamber on the shoulder of the cartridge case. 4. RIMMED: A type of chamber design in which the cartridge seats in the chamber on the rim or flange of the cartridge case.

HEADSPACE GAUGE
A device used in a firearm to determine the distance between the breech face and the chamber surface on which the cartridge seats. Also called Breeching Plug.



Now if you want to go back 80 years, in 1937 Phil Sharpe described "headspace" as what SAAMI now defines as "head clearance."
But by the 1949 revision/addendum to 'Complete Guide to Handloading' he had gone over to the present usage.
So there is a little history for you.

I will further note that F.W. Mann described his "Hamburg Rifle" as having no headspace/head clearance/"backleash" because its interrupted thread locking lugs "screwed the breechbolt right up to the head of the cartridge."

Target shooters used to like the Ballard single shot because it could be fitted to zero head clearance with a particular lot of ammo.

Me? I think it best to just take "headspace" as a term of art and not worry about its etymology.

If you just must, you will get a lot of verbiage from F. Guffey's posts.
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