Yes, I really mean head space.

[fguffey]

Is .004 HS too much in my M70 ?" Hard to answer if you really mean "HeadSpace, but .004" end-play is no problem.

Parashooter, you have been here for over 20 years, in those 20 years I feel like I have failed you. You start with a question about the head space in the
30/06 chamber of your Model 70 Winchester. You claim the head space is .004" and you want to know if .004" is too much head space?

If your rifle chamber has .004" head space you have the skinniest chamber in the world. After 20+ years you should understand the head space of the chamber is measured from the datum to the bolt face. The datum for the 30/06 family of chambers is .375". I know, your chamber drawings read 'datum line', I do not care how you look at the datum, it is a circle, it is a round hole, it is not a line.

Move on to clearance: After 20 years you want to take it to end-play. Without a case there is no clearance, there can be no end play, THE LENGTH OF THE CHAMBER IS A MEASURMENT; if THE SMITH IS MEASURING THE LENGTH OF THE CHAMBER FROM THE DATUM TO THE BOLT FACE AND IF THE HEAD SPACE GAGE IS THE CORRECT LENGTH IT WILL NOT HAVE NOR CAN IT HAVE ANY END PLAY.

For me? Not a problem but chambers are not all identical, some are long, some are short. For years upon years reloaders have insisted the case has head space. Bart B. called SAAMI and told them they made a made mistake, I told Bart B. the case does not have head space and then I suggested he read the SAAMI drawings of chambers and cases. SAAMI list head space for the chamber but they have never listed head space for the case. I have found 'full length size' and minimum length case. And then? That is where the .004" measurement comes from. In the perfect world the case when measured from the datum to the case head is .005" shorter than the length of the chamber from the datum to the bolt face.

And then one day I decided it is possible to measure the length of the chamber from the datum to the bolt face without a head space gage so I made a tool that allowed me to measure the length of the chamber from the datum to the bolt face with a end-play measuring tool (with the bolt closed)

F. Guffey

[Parashooter]

Hello Mr. Guffey. I suspect you're confused about the origin of the dispute. The bit you quoted from my post of 2/6/22 was in reply to a question from "Milboltnut" -

milboltnut

Is .004 HS too much in my M70 ? I start with 2.046 and have to size to 2.042. Funny the NG gauge is 2.046 and doesn't come close to the bolt closing and the go gauge is 2.042 which the bolt has very slight resistance on closing.

Is the 06 hard to deal with HS wise ?

Last edited by milboltnut; 02-05-2022 at 10:13.

Truth be told, I seldom disagree with the facts you present in your posts, but do wish you would work on untangling your prose and avoiding a tone readers sometimes perceive as belligerent.

Certainly the "datum" is a circle, but it's dimension is expressed as diameter, the length of a line from one side to the other, through the center. Can't it be both a line and a circle?

Years ago I too used "clearance" to describe any axial space between closed bolt face and chambered cartridge head.
Headspacerest.jpg

After coming across this drawing in a classic text -
HeadspaceJH.jpg

I decided to try "end-play" as more specific - for rimmed and rimless designs.
Headspace.jpg HeadspaceC.jpg

I'm open to a better term if you have one handy.

[fguffey]

And then one day I decided it is possible to measure the length of the chamber from the datum to the bolt face without a head space gage so I made a tool that allowed me to measure the length of the chamber from the datum to the bolt face with a end-play measuring tool (with the bolt closed)

And then one day I was in Jeff Lee's Gun Parts Store, while there a gun owner with a magnificent rifle wanted it checked for head space measured. Mr. Lee did not have a head space gage for the customer's rifle, he left. After he left I told Jeff Lee I could measure the length of the chamber for any rifle without a head space gage. Mr. Lee just ask "HOW?" I demonstrated one method and I explained to him how it was possible. He gave me his short speech, he said "I be dammed". I understood it was not worth his time because he does not charge for checking the length of the chamber.

And then one day I decided it is possible to measure the length of the chamber from the datum to the bolt face without a head space gage so I made a tool that allowed me to measure the length of the chamber from the datum to the bolt face with a end-play measuring tool (with the bolt closed)

After coming across this drawing in a classic text -
Click image for larger version.

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On your drawing from the classic text I noticed there was a big spread between the listed clearance and rim, The rim is limited by the thickness of the rim, as you know we all measure. In what appears to be clearance at the case body/shoulder juncture is an area that will be blown out when the round is fired. I know there is that thing called case head separation, to avoid being called belligerent I want to thank you for the kind words

Truth be told, I seldom disagree with the facts you present in your posts,

F. Guffey