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".

[lyman]

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

[fguffey]

Purchased mine from Sinclair and I am well pleased. FWIW

Sinclair and Hornady had a problem with their methods and technuiques when making gages. Helping Sinclair or Hornady with suggestions did not work; years ago Jimmy Dean talked about getting the opossum across the road safely. He thought it would help if he was able to convised the possum ‘IT COULD BE DONE”.

So he asked: “Why did the chicken cross the road?”, as expected no one knew so he explained; the chicken crossed the road to show the opossum it could be done.

Well there is no showing Hornady/Sinclair it can be done. A reloader can not verity the accuracy of the Hornady comparator, information gathered from the tool does not agree with any reloading manuel or SAAMI.

‘WHY?’ The hole in the tool is not a datum, the hole in the tool has a radius, I understand no one understands what that means but the datum does not have a radius; my datums have sharp edgesm my datums are not case friendly.

Back to the Wilson case gage, the Wilson Company uses datum with a raius but they understood how to make a tool that could be verified. The first case gage I examined got the treatment, I stood the gage on a block of lead and then drove a case into it; when finsished the case head was .100” below the open end of the gage, after driving the case gage the datum with the radius was well defined.

L.E. Wilson, what a bunch of geniouses.

Again, I make datums, I have purchased datums, my datums are not case friendly, I have a grinder, I can use it to make pilots, I can grind angles and I gan grind ‘to length’. If it was necessary to shorten a die and or lower the deck height of a shell holder I have the grinder if it was necessary. Problem, when the cases are removed from my press I can determine if the case was sized, nothing special but I can determine if the case is full length sized before I lower the ram amd I can determine if it necessary to grind the bottom of a die and or shell holder.

F. Guffey

[JOHN COOK]

Again, I make datums, I have purchased datums, my datums are not case friendly, I have a grinder, I can use it to make pilots, I can grind angles and I gan grind ‘to length’. If it was necessary to shorten a die and or lower the deck height of a shell holder I have the grinder if it was necessary. Problem, when the cases are removed from my press I can determine if the case was sized, nothing special but I can determine if the case is full length sized before I lower the ram amd I can determine if it necessary to grind the bottom of a die and or shell holder.

Guffey, you should be working for NASA. I knew when I posted about the photo in the American Rifleman I was on thin ice. I knew you would not be able to pass up an opportunity to show us all your knowledge on headspace. It's the same rhetoric as your pass posts. S A A M I drawings shows the chamber of a 30:06 Datum line being .375 ( that is a diagonal dimension) and labels it HEADSPACE DIMENSION . The length from this Datum line to the base of the cartridge, as shown on the drawing, is
2.048 Min. and 2.0587 Max. It states very clearly that this is required to get proper Headspace on the 30:06. On the same page is a drawing showing dimension for the 30:06 cartridge. It shows the Datum line being .375 Basic. You are correct, the drawing does not refer to headspace. This drawing also shows the Dimension of 2.0526- .0070. from the Datum line to the base of the cartridge. A little math and it shows the Datum line on the cartridge can be 2.0526 and minus .0070 which gives you a length of 2.0456. It is very clear to me the .375 Datum line being the same on both drawing is relevant.

By the way since you can BUY Datums , please send me a box full. I wish to reload next week and you can never have to many DATUMS.. I'm done with this.

john in SC

[nf1e]

Getting involved in the technical mumbo jumbo could really take the fun out of the hobby. I would much rather hear comments from grass roots loaders if there are any left on this side of the sod.
The Boogie Woogie google boys are welcome to their slide rules and fancy jargon. Doesn't make my ammo shoot any better and that's all I have been interested in.

[fguffey]

Guffey, you should be working for NASA. I knew when I posted about the photo in the American Rifleman I was on thin ice. I knew you would not be able to pass up an opportunity to show us all your knowledge on headspace. It's the same rhetoric as your pass posts. S A A M I drawings shows the chamber of a 30:06 Datum line being .375 ( that is a diagonal dimension) and labels it HEADSPACE DIMENSION

I off set the length of the chamber with the length of the case, for me it is easy because I measure the length of the case from the datum to the case head. The only way that is possible is to know the length of the chamber from the datum/shoulder to the bolt face.

Reloaders and smiths though that was all that was required, they did not have a clue. The datum is a round hole, the datum is a circle, the round hole for the 30/06 is 3/8” or a .375” diameter circle.

‘HEADSPACE DIMENTION’ “and that is how they do it” ? A reloaders needs to know the diameter of the diameter of the datum to determine the length of the chamber; and length of the case from the datum to the case head. A smith/reloader that can drill a round hole with a diameter of .375” and can verify ‘ZERO’ can determine the length of the case from the datum to the case head.

It has nothing to do with me not being impresses with all of your numbers; all we are doing is measuring from a datum; the datum must be ‘ZERO’. Back to Hornady and Sinclair, they use a radius on the datum; the radius puts the datum/diagonal below zero.

‘Back to my same old rhetoric’ L.C. Wilson has been making case gages for over 81 years, during all of that time they have used a radius on the datum based case gage. A reloader is not required to think when using a case gage because Wilson grinds the case gage to the correct length for minimum length sized cases and cases that are go-gage length from the shoulder to the case head. But to most reloaders the Wilson case gage is a drop-in gage.

To verify the Hornady comparator the reloaders should be able to determine if the tool can be zeroed. I have no interest in breaking anyones mind bit there are transfeers and standards like the headspace gage that can be used to verify.

Life for me is much more simpler because I do not use a radius on the datum. In the real world the hole in the datum is drilled undersized and then renamed to diameter. I know, reloaders just love their Sinclair/Hornady comparator.

I was thinking about a new datum based tool yesterday, and then I decided there is not one reloader on this forum or any other forum that would understand the function of the tool or appreciated the speed.

F. Guffey

- - - Updated - - -

Guffey, you should be working for NASA.

Forgive, thank you.

F. Guffey