Headspace Guage Questions

[RobbRus]

Good day everyone. I'm starting a build project in the near future and will be needing 7.62x39 Headspace Gauges.

I see SAAMI spec as well as CIP. What is the difference between them and is one superior to the other?

Also, from the suggestions in a couple other threads, I can make some educated guesswork of brands to get. But does anyone have any other info or recommendations?

Thanks in advance.

[ar15barrels]

Good day everyone. I'm starting a build project in the near future and will be needing 7.62x39 Headspace Gauges.

I see SAAMI spec as well as CIP. What is the difference between them and is one superior to the other?

Also, from the suggestions in a couple other threads, I can make some educated guesswork of brands to get. But does anyone have any other info or recommendations?

Thanks in advance.

SAAMI specs are specified with a shoulder angle and a datum diameter and length.
CIP specs are specified with a shoulder angle and a length where the two lines converge.
You can draw the exact same case dimensions using either system.

There is no advantage to one or the other.
Just get headspace gauges made by the same manufacturer for the same cartridge so they are made in the same method.
Do not mix gauge brands in a single chambering.

[RobbRus]

Thank you Randall and have a good one.

[TFA777]

The Sinclair gauges go off the shoulder, the Hornady go off the datum.
I believe the Sinclair are more consistent because it's not a single point on the shoulder that you're headspacing from.

But that's my theory

[ar15barrels]

The Sinclair gauges go off the shoulder, the Hornady go off the datum.
I believe the Sinclair are more consistent because it's not a single point on the shoulder that you're headspacing from.

But that's my theory

A datum is typically a diameter and a length that occurs on a taper when we are talking about case shoulder lengths.
As an example in the print below, the headspace datum is 1.4717" long and 0.375" diameter:

[fguffey]

Also, from the suggestions in a couple other threads, I can make some educated guesswork of brands to get. But does anyone have any other info or recommendations?

It appears you are headed for the plus and minus method that is combined with tolerances, that works for the undecided. I would suggest you learn to work with micrometers and gages. I have no idea where all of these different head space gages come from, they all should be the same size. I also suggest you learn how to zero your tools.

F. Guffey

[kendog4570]

... they all should be the same size....F. Guffey

It's getting downright spooky, I am agreeing with you.

A gauge is a gauge,....is a gauge....




Except of course if you ask the CMP and you get the "Clymer Only" drivel about M1 rifles and 30 M2 chambers and gauging.


I'm thinking Max Clymer has pictures of Orrest screwing a goat, therefore the plug for their brand.

[Toxic Shock]

kendog4570: You're the one that I got the idea of using a 7.62x39 Lapua spec. reamer from! BTW: 1 MOA accuracy from a .308 dia. barrel, so thanks.

[kendog4570]

kendog4570: You're the one that I got the idea of using a 7.62x39 Lapua spec. reamer from! BTW: 1 MOA accuracy from a .308 dia. barrel, so thanks.

Excellent! Still haven't built mine yet. Got the reamer, action, stock, and barrel. A case of the shoemakers kids go without shoes. One of these days...


I'd love to claim I thought it up all by myself, but it came to me from Ed Harris (CE Harris) one of the design engineers at Sturm Ruger for the MIini 14. He has been published in many a journal and periodical for many years. Unlike a lot of gasbag gun writers, when one hears Ed speak, one listens.

[SVT-40]

Get an original Soviet made set! They are available.

Russian AK, SKS and RPD gauge kit. It has three head space gauges in it. They are :

K-3 "pass" 32.85 mm
K-4 "impassable" 32.95 mm
K-5 "defective" 33.155 mm

Link to thread on these and the other tools and gauges in the kit.

http://www.calguns.net/calgunforum/showthread.php?t=1587249

They were made in 1952, along with the rest of the kit.

[fguffey]

The Sinclair gauges go off the shoulder, the Hornady go off the datum.
I believe the Sinclair are more consistent because it's not a single point on the shoulder that you're headspacing from.

But that's my theory

TFA777

My cases do not have headspace, reloader believe everything and every tool and gage have head space. My chamber has a head space dimension. Many reloaders purchased a dial indicator stand/holder advertised as a digital head space gage.

The Sinclair tool qualified as a case comparator because the maker did not know how to make an accurate tool. The problem was with the datum on the tool. The 30/06 family of chambers use the datum 3/8" or .375". Manufacturers of the comparator gage put a radius on the datum, I can only guess the radius on the datum was designed to be more case friendly, that did not happen, the radius reduced the diameter of the datum.

Anyhow, that is the reason the Sinclair etc. tool is called a case comparator and because reloaders believe ever tool is a head space gage etc. etc.

These tools are so simple to make if the reloader understands how to make the tool.

F. Guffey

[fguffey]

SVT-40, I have a tool that will make gages to measure chambers, it is impossible concept to sell because reloaders believe they have to have three gages. the go, the no and the beyond.

F. Guffey

A friend had close to 25 head space gages for the 30/06 chamber; he built a 30/06 rifle and then could not measure the length of the chamber, he wanted go-gage length.

I offered to make him a go-gage that measured from go-gage length to infinity; he said no, all he wanted was a gage that would allow him to measure the length of 'HIS' chamber.

I called him the other day just to check on him, he did not remember me.

F. Guffey

[kendog4570]

YAWN......