Headspace question- check my work

Point was, you will find small variations in these dimensions between manufacturers, so in the interest of consistency it is best to keep to the same one.
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I received a call from a smith in North Texas that was starting to build one of his custom rifles, he had a no go gage but did not have a go gage. I explained to him he did not need the go-gage. I explained to him he could measure a short chamber, a go-gage length chamber and a no go-gage length chamber with a no go-gage. Variations and inconsistencies between gages and manufacturers is not a problem if the person using them can verify, I am the fan of verifying, I am the fan of standards and I am the fan of transfers.

That was not my point. "Measuring" the exact length to the gauge datum is not so simple (but please enlighten me if you know something I do not) but can be done with reasonable accuracy with a comparator- but even that is not exact as these are not precision ground for extreme accuracy.
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I do not make excuses for not being able to do it. Like I said, the collector building the Rock Island 03 had 20 30/06 head space gage, not one of the 20 would measure the length of the chamber; but I could use any gage in his collection to determine the length of the chamber. Some of the gages went back to the beginning when the datum was on the case body/shoulder juncture.

F. Guffey
 
tobnpr, we rarely agree on anything, but you are absolutely on the right track. I worked on guns in the military and told people for years that the headspace on the .308 and 30-06 was not the same as SAAMI dimensions. You always get guys that "Know". When you get into CIP specs, it really gets weird. What it boils down to when using gages is, will the gun be safe? Even that is not an exact call. Take your favorite rifle, the 7,62x54R. Using the standard HS gage, you are basically not checking headspace at all. You have no idea what kind of dimensions are in front of the rim. I used to have access to a comparator, and they are wonderful things, but you are splitting a fine hair with gages. The most accurate way to check is to double bore a ring to the intersection and body size, grind, and use a manual mic. Grinding shops have come a long way now with CNC grinders. Or, you could use Guffy's magic tape measure.
 
What it boils down to when using gages is, will the gun be safe? Even that is not an exact call. Take your favorite rifle, the 7,62x54R. Using the standard HS gage, you are basically not checking headspace at all. You have no idea what kind of dimensions are in front of the rim.
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Back to the M1917 and the long chamber, I could have fired new ammo in the rifle, but after firing the cases would have been short from the end of the neck to the case head. And then there is your claim of unsafe and what it boils down to is the use of gages. I believe it has as much to do with understanding what happens to the case when the trigger is pulled. When the trigger is pulled on a short case in my M1917 the case does not separate nor does the shoulder move meaning there is no stretch between the case head and case body when fired.

In the beginning there was the rim and later the belt. Both were designed to hold the case to the rear and anything that happened in front of the rim and or belt was if little concern. The purpose of the case body was to expand and seal the chamber. One example is the 303, no one measures the thickness of the rim and no manufacturer sells cases with different rim thicknesses. And it always goes back to the gage. Head space gages are available for the 303 and belted chambers with different thicknesses, I can measure all of the differences in head space on rim and belted chambers with one gage for each, I had no ideal that was called magic. But I have always wondered why smiths and reloaders have such a huge infatuation with head space gages that only measure go and or no go. I do not believe go or no go was all reloaders and smiths needed to know.


Again, it seems when the bolt closes the lights go out and the chamber gets dark.

F. Guffey
 
Grinders; I have grinders

The most accurate way to check is to double bore a ring to the intersection and body size, grind, and use a manual mic. Grinding shops have come a long way now with CNC grinders. Or, you could use Guffy's magic tape measure.
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I have three grinders, they grind in-line, at an angle and grind to length or butt-cut. Handy when making pilots, tapered gages or tapered pins or putting an angle on a taper and grinding to length.

F. Guffey
 
Well Guffy, when you actually acquire some knowledge of what goes on in a chamber when you fire off a round, I may bother to discuss this further.
 
Well Guffy, when you actually acquire some knowledge of what goes on in a chamber when you fire off a round, I may bother to discuss this further.
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Why is it a bother? All you have to do is explain what 'THE Guy' needed to know about his M1917. The M1917 is notorious for having a long chamber. There are experts that have narrowed the search for blame to one smith, they blame him, not because he 'did it' but because they did not understand what he was going and they would not ask him.

F. Guffey
 
But I have always wondered why smiths and reloaders have such a huge infatuation with head space gages that only measure go and or no go. I do not believe go or no go was all reloaders and smiths needed to know.
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I'm sure no one would dispute this. Esp in the case of a rimmed cartridge, as was mentioned, there could be a cavern the size of an egg where there should be a chamber, and the barrel shoulder can still be set back to headspace perfectly with the gauge and bolthead.

Which is why, if I have the opportunity- the reamer and hs gauges will be from the same manufacturer as well. Especially in the case of the 54R, there is wide variation in gauges. The rim on my PTG "no-go" is .0695, on the Okie it's .0735 allowing a lot more tolerance for "acceptability". Matters not unless checking a rifle for safety anyway, as new barrels are set as close to .001 over "go" as I can get.
 
I used to bore the rim area into the barrel face and then go in with a reamer that had no rim cutting area. Used cellophane off a cigarette pack between the rim of the case and the barrel face. When it caught, it was good. This will give you a really tight chamber with rimmed rounds. Really, you can bank off the shoulder if you want to. The 7.62x54R case is easily strong enough to do that.
 
Gun plumber what would be a substitute for cigarette cellophane? I don't smoke and not really want to spend money for a pack of cancer sticks.
 
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