Headspace & Head Clearance - Not The Same According To SAAMI

Bullet94 · March 25, 2008, 01:00 AM

Quote:

Quote from SAAMI -

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.

http://www.saami.org/Glossary/index.cfm

Does SAAMI have this wrong?

Headspace is a characteristic of a chamber( not a case, or ammunition). it is specified on the SAAMI chamber drawing( and not on the cartridge drawing).

There are minimum and maximum chamber dimensions... (the rifle makers use) - Headspace

There are minimum and maximum cartridge dimensions... ( the die makers use) - Which effect Head Clearance - (Commonly confused with headspace).

freakshow10mm · March 25, 2008, 01:03 AM

No it's right.

wncchester · March 25, 2008, 08:15 AM

SAMMI not only approves the dimensions they also provide the definitions. Most of the rest of us only get it screwed up.

brickeyee · March 25, 2008, 09:02 AM

The SAAMI definition is assuming the catridge is fully forward, thus making the 'gap' between the breech and the base of the cartridge.
This is how it is actually measured.

Phil218b · March 25, 2008, 04:32 PM

Headspace is the dimension of the breech face to the shoulder of the cartrige contact in the chamber. Head clearance is the space that allows the cartride to safley expand when fired. Each brass cartridge will expand when heated by the explosion from firing, it shrinks back before extracted this can be seen by small imperfections in the brass after firing which will make each chamber unique to each firearm. If there is no space after a few shots the expansion of the barrel would lock up the action untill it cooled down, causing extreme pressure. To much space will cause the brass to stretch and become thin and rupture. Either one can be dangerous. I always think about 50,000 lbs. of pressure, 3 inches from my cheek, as a concern for saftey

March 25, 2008, 04:32 PM	#5
Phil218b Junior Member Join Date: October 8, 2006 Posts: 2	headspace Headspace is the dimension of the breech face to the shoulder of the cartrige contact in the chamber. Head clearance is the space that allows the cartride to safley expand when fired. Each brass cartridge will expand when heated by the explosion from firing, it shrinks back before extracted this can be seen by small imperfections in the brass after firing which will make each chamber unique to each firearm. If there is no space after a few shots the expansion of the barrel would lock up the action untill it cooled down, causing extreme pressure. To much space will cause the brass to stretch and become thin and rupture. Either one can be dangerous. I always think about 50,000 lbs. of pressure, 3 inches from my cheek, as a concern for saftey

March 25, 2008, 01:03 AM	#2
freakshow10mm Junior member Join Date: January 23, 2008 Location: MI Posts: 1,398	No it's right.

March 25, 2008, 08:15 AM	#3
wncchester Senior Member Join Date: December 1, 2002 Posts: 2,832	SAMMI not only approves the dimensions they also provide the definitions. Most of the rest of us only get it screwed up.

March 25, 2008, 09:02 AM	#4
brickeyee Senior Member Join Date: December 29, 2004 Posts: 3,351	The SAAMI definition is assuming the catridge is fully forward, thus making the 'gap' between the breech and the base of the cartridge. This is how it is actually measured.