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View Full Version : What exactly is "headspace" ?


mhannah1
October 1, 1999, 12:56 AM
I hate to sound like an idiot, but, I keep hearing about this thing called "headspace" in reference to whether a gun is safe to shoot. (obviously I have some room in my "headspace" for some more gun learnin')

George Stringer
October 1, 1999, 07:12 AM
Though it's measured from different points for rimless, rimmed, and belted cartridges headspace is the distance from the rear of the cartridge to the face of the bolt when the action is closed. George

James K
October 2, 1999, 11:25 AM
George is correct, but maybe he won't mind my adding a little background. Oddly, the "head" of a cartridge is its base or back end. (This is not the same as having one's head up... never mind.) That's why the markings on the back of the cartridge case are called the "headstamp".

So, headspace is simply the space for the "head" of the cartridge. In a rimmed cartridge, this is obvious, but for rimless cartridges, it really is a measurement of the room for a cartridge from the bolt face to whatever stops and supports it in the chamber. For cartridges like the .308, measurement is taken from a point on the shoulder; for a cartridge like the .45 ACP, the measurement is from a sharp shoulder which abuts the case mouth. So we say that a .308 headspaces on its shoulder, and that a .45 headspaces on its case mouth.

Headspace is critical in that if excessive it can allow a case to stretch so much when fired that it will, at best, make the case unreloadable, and at worst allow the case to separate and let high pressure gas loose in the action. The latter condition will damage the rifle and could cause serious injury to the shooter. The opposite condition, not enough headspace, will not allow the cartridge to seat fully or the action to close.

Headspace can increase with wear and extensive firing. It is checked with gages. The action must close on a "GO" gage, and not close on a "NO-GO" gage. The military uses a third gage, a "FIELD" gage, and removes from service any rifle that will close on it.

While firing does affect headspace, a good rifle (such as the M1) will accept thousands of rounds without showing any significant increase in headspace.

Hope this helps.

Jim

Jim V
October 2, 1999, 06:07 PM
Gee, I always thought headspace was your hat size. LOL :D

------------------
Ne Conjuge Nobiscum
"If there be treachery, let there be jehad!"

James K
October 4, 1999, 10:11 PM
My cap says "one size fits all". Doesn't work for headspace.

Jim

Bennett Richards
October 5, 1999, 01:09 AM
Is headspace important in shotguns?

George Stringer
October 5, 1999, 06:58 AM
Bennet, headspace is as important in shotguns as any firearm. George