Determining Headspace ETC... ETC

[JOHN COOK]

There is an article in the American Rifleman (November 2019 page 41) explaining how to properly obtain the correct measurement to the Datum line of a resized case using a tool sold by Hornady. This tool was originally manufactured by Sinclair Products.
I am not posting this to argue the point of Datum line measurements or headspace. I only want to bring up the photo which accompanies this article. What they explain in the article is misrepresented in the photo. The photo is not showing what they are trying to explain. The photo shows the tool being used to measure the depth of a bullet when inserted into a correctly formed case, not to the Datum line. This could be confusing to someone who might purchase this tool. I have used one for about 10-12 years. Purchased mine from Sinclair and I am well pleased. FWIW

john in SC

P.S.
I am just guessing I may get a reply by someone how they use "FEELER GAUGES" to set up dies to get correct headspace etc.. PLEASE PLEASE ***

[nf1e]

Totally agree. When I read the article, I thought to myself, what the hey. Wrong photo for what he was trying to explain.

I use that tool for setting seating depth from the lands along with a micrometer seating die, not determining headspace.





The RCBS precision mic is a useful tool for measuring headspace and setting sizing dies. My preference is .004 under chamber size for my auto loaders.

[JOHN COOK]

I use that tool for setting seating depth from the lands along with a micrometer seating die, not determining headspace.

Yup, that will work...

john in SC

[Sunray]

"...not determining headspace..." That's because 'head space' is a rifle manufacturing tolerance only. Cartridges do not have headspace. There is no "measuring" headspace either. You cannot adjust or compensate for bad head space by fiddling with the case length.

[nf1e]

"...not determining headspace..." That's because 'head space' is a rifle manufacturing tolerance only. Cartridges do not have headspace. There is no "measuring" headspace either. You cannot adjust or compensate for bad head space by fiddling with the case length.

Is that a Canadian joke?

If not I have been doing it wrong for over 50 years my friend. This is a critical measurement that is easily checked with proper equipment. There is chamber headspace measurement and cartridge headspace measurement. I like to set my cartridge headspace .004 under chamber headspace for auto-loaders and a little tighter for bolt rifles.

Headspace = distance between the bolt face and a datum line (determined by SAAMI) where the front of the cartridge rests on its shoulder when the bolt is closed.

[Parashooter]

HeadspaceCquiz.jpg

Many believe headspace is a measurement of the space within the chamber - not the size of a cartridge occupying that space, nor the difference between the two. Others disagree - leading to all manner of confusion.

[nf1e]

I guess it is whatever one would like it to be. That would make everyone correct and all get a gold star for participation. Sign of the times.

[lyman]

I guess it is whatever one would like it to be. That would make everyone correct and all get a gold star for participation. Sign of the times.

I used to follow the mantra of all headspace gauges are created equally, never lie, and should be used and if a rifle fails, be rebarreled,

after a few thoughtful conversations, (both as a follower and a participant) on a couple forums (including this one years ago) I came to realize that mantra was too rigid,

I think a lot of folks get confused sometimes (myself included) on what headspace measures, and what that means to the reloader,
and that a good reloader can adjust his dies to have the brass fit the headspace on a rifle, even if the field gauge says the rifle is toast,

exceptions abound, safety is paramount, proceed with caution, etc etc

[fguffey]

If not I have been doing it wrong for over 50 years my friend. This is a critical measurement that is easily checked with proper equipment. There is chamber headspace measurement and cartridge headspace measurement.

The case does not have head space; SAAMI does not use the symbol for head space in their case drawings. SAAMI does use the symbol for head space in their chamber drawings.

One reloaders spent a lot of time promoting the idea the case had head space. And then one day someone introduced him to SAAMI; if SAAMI did not agree with them he decided they were wrong. And then one day he called them, I am sure they were impressed with whom he was and all of his accomplishments but from the beginning the case has never had head space. There is only one measurement that is the measurement from the datum to the bolt face. If there is a difference between the length of the chamber from the shoulder/datum to the bolt face and case from the shoulder of the case to the case head it is called clearance.

And then there is the inflated opinion of one’s self. I have fired 8mm57 rounds in 8mm06 chambers. I have no ideal what is so difficult for a reloader to understand but the clearance between the 8mm57 when fired in an 8mm06 chamber is .127”. If there was any truth to what parashooter posted the firing pin would never make it to the primer if the case of the shoulder was against the shoulder of the chamber. A reloader that knew what he was talking about should be able to explain where the case was when fired by the length of the case from the shoulder to the case head and the length of the neck from the end of the neck to the shoulder/neck juncture.

I understand; it is a mind boggling thing but the neck of my 8mm57 cases when fired in an 8/ 06 chamber disappears (almost) and the case length from the datum/shoulder to the case head increases .127”.

I have another rifle with a 30/06 chamber, the chamber is .016” longer from the datum to the bolt face, Again (mind boggling), if I fire a minimum length/full length sized over the counter new ammo in that chamber there is .016” clearance and the clearance is not between the bolt face and case head. When I fire minimum length/full length sized ammo in that chamber the case increases in length .016” between the datum/shoulder to the case head and shortens between the shoulder/case neck juncture.

It is not my fault this stuff is beyond a smiths/reloaders comprehension. From the beginning reloading forums have had too many members that were and are too desperate for attention. I do not need the attention, for years and years reloaders have identified the Wilson case gage as a drop in gage. The Wilson case gage is not a head space gage, it is a case gage.

F. Guffey

[nf1e]

From BC " It all depends on what the meaning of is is".