Headspace & Head Clearance?

[Bullet94]

Recently I found these,quotes listed below) in SAAMI’s Glossary -

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.

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.

I found these on another web site and they seem to be conflicting in regards to headspace and head clearance. According to SAAMI which would be correct? And why?


1 -

Headspace is exactly that. How far the case has available to stretch back to the breech face. It can not be too far or it is dangerous, obviously. That is why we have SAMMI limits for chambers and ammo. The handloader has control over how far he pushes the shoulder back, thus they controls headspace.

2 -

If a rifle has the headspace set correctly by the manufacture according to SAAMI’s specs then the only thing a reloader can effect by resizing their case would be head clearance.

 

[Rustystud]

Not only is "headspace, case clearance", mis-labeled so are the gauges and indicators used to measure them.

Head spacing gauges are steel and are known as "go and no-go gauges". Case gauges are exactly that "case gauges".

This is not to confuse the relationship between the two.

Rustystud

 

[Lucky Shooter]

Per SAAMI----"Headspace" dimension only applies to the chamber.

As has been said here many times, we throw the word around as applied
to cases but we understand each other's language.

I'd never noticed the term "Head Clearance". Thank you for calling this out.

Sometimes it pays to make sure you and the other guy are talking the same
language.

A. Weldy

 

[Herzo]

Headspace and head clearance are opposite ends of the same measurement. If the cartridge is seated on the shoulder of the chamber, then the distance between the base of the case and the face of the bolt could be called head clearance.

 

[Bill Norris]

Headspace and head clearance are opposite ends of the same measurement. If the cartridge is seated on the shoulder of the chamber, then the distance between the base of the case and the face of the bolt could be called head clearance.

That's exactly how I understand it as well.

 

[divingin]

Per SAAMI----"Headspace" dimension only applies to the chamber.

As has been said here many times, we throw the word around as applied
to cases but we understand each other's language.

Part of that is because, despite each having it's own measurement, neither is important until you put them together.

As an example, you can have, say, a 308 rifle with a 4" chamber, and a 308 cartridge that measures 1" from base to shoulder. Neither will fail until you actually try to use them together.