30-06 Headspace differences

[WineMan]

Another question.

When reading Hatcher's Notebook he gives the headspace for the 30-06 as minimum of 1.942" and the field of 1.950". His case length is the same as recorded in several reloading manuals as 2.494". Current Forster SAAMI spec gauges are 2.049" GO and 2.058" Field. The difference between the Min/GO and Field is 0.008" for both. It looks to me as if the numbers from Hatcher were to the beginning of the shoulder rather than a mid point of the shoulder. If you subtract the rim thickness of 0.049" the numbers do not match. I have tried the math several different ways and can not come up with something that makes sense to me

However Hatcher's numbers for the 270 Win at 2.048 minimum seem to match with Forster's at 2.049" for GO.

This is not a huge deal but was there a change when SAAMI came out with their specifications?

Thanks in advance,

Wineman

[mike in co]

commercial .30'06 and mil .30'06 are measured differently.

maybe he confused the two, or misspoke on one, or did not know there was a difference.

saami is 2.0487 min and 2.0587 max.

moving from 4 to 3 significant digits may have led to part of the problem also.

mike in co

[WineMan]

From the context I assume he was dealing strictly with Military chambers and not sporting arms. I just wondered why the differences for the same caliber.

Wineman

[mike in co]

you will have to ask the government......they are the ones that chose to use a different std when defining the chamber/headspace of the 30-'06

[NoDakJak]

You have to remember that Hatcher was speaki ng in reference to the experiences of WW! where rifles had to hadle the mud, crud and blood od the muddy trenches. Cartridge length was extended to handle the crud and stil allow the bolt to close. They sure as hell weren't worried about reloading cases. The 303 British rifle sometimes had obscenely long chambers. I have a couple 303 Ross rifles where the cases resemble crude 303 improved cases. I have owned many of the great 1917 Enfield rifles and all of them had chambers that are considered to have excessive headspace by modern standards. No such thing exists for the knowledgible handloader. Simply seat your bullet out to touch the lands and fire form your cases. Most of the Remington Rolling Blocks in 7x57 are considered to have excessive headspace. Whoa Hoss! The Rolling Block has zero camming power! Whatcha gonna do when yer in combat and you can't get the block to close on a cartridge that has a few flecks of dust on the case? Yowza! Enlightenment! Word to the side: Every one of the 1917 Enfields that I have owned had outshot gthe 1903 Springfields that I have owned. Blasphemy! Ah well!

[Char-Gar]

You really don't need to worry about the dimensions on a "Field" gage. It is the "Go" and "No Go" gage dimensions you need to concern yourself with.

The "Go" gage is the minimum chamber length to accept ammo made to proper specs. The bolt on a properly headspaced rifle should close on the Go gage with a slight feel of drag.

The "No Go" gage, is longer than the Go and a properly headspaced rifle should not close on the No Go Gage.

The "Field" gage is a military field gage that is longer than No Go gage. It represents the longest headspace dimension the rifle should have to remain in service. A rifle should not close on the Field gage, and if it does, it has a headspace problem that needs tending to. A rifle that closes on the Field gage may or may not represent a danger to the shooter, depending on how much longer the chamber is than the Field gage.

The 30-06 cartridge has been around a long time and some of the published specs predate current headspace standards.

It should also be noted that many military headspace specs are in excess of civilian specs. This is done to create a chamber that will still function under combat conditions, which might include ammo with a little dirt or mud on the ammo, or a dirty chamber from prolonged firing.

[Phil]

Actually, some years ago, for whatever reason, SAAMI changed the location of the datum line on the 30-06 cartridge. Dimensions of gauge and chamber were never changed, just the datum line.

Cheers,

Phil

[Larry Gibson]

Phil's answer is correct. Chamber dimensions are the same, just a different datum line on the shoulder gives a different measurement.

Larry Gibson

[WineMan]

Makes sense now that the point of measurement was changed.

Wineman

[M98]

diff from reg...if you get mil mg 308s...you should resize with sb dies...a combat rifle or pistol is LAYOOOOOOSE.. match real tight...and reg is in the middle..

[mike in co]

diff from reg...if you get mil mg 308s...you should resize with sb dies...a combat rifle or pistol is LAYOOOOOOSE.. match real tight...and reg is in the middle..


not sure what that has to do with two different specs for .30'06 headspace...???
and dont use a small base die till you know a std will not work. unecessary over sizing of brass will cause an early death of the brass.

blanket statements of "what to do" for a given situtation ....is a silly approach.....do what works for you in your situtiation.

now we have a "combat" pistol chambers ???

mike in co.

[M98]

everything is built to a spec...a mil sloppy rifle is not a match...why?? tighter specs in the build...buy a match reamer..is it the same as reg?...nope..the m1 garand will shoot factory ammo..its not the same size as mil ammo but it works.