Can someone give me the skinny on this?  Where is the best place to buy rifle headspace gauges and how are they used?

There's certainly nothing wrong with headspacing a surplus gun, and if you want the guages go to Midway or Brownells. Basically you have 2 guages which go into the chamber like a cartridge. They are marked "go" or minimum and "no-go" or maximum. The maximum guage is a guage that is too large, or would indicate that the headspace is excessive. The "minimum" is a the opposite, it indicates that the headspace is enough, but not too small.

How they work is, you chamber the "go" guage, the bolt should close easily on it. Then, you chamber the "no-go" headspace guage. The bolt should NOT close on it. If it does, then the headspace is excessive. That's the short answer.

That said, I have never nor will I ever headspace one. I put the gun on the bench, put a sandbag over the action, duck my head below the bench and fire the gun. Then, I see if the round is hard to extract, has any visible signs of cracking, pressure rings or pierced primers. If everything's cool, the case looks good, guess what? It's got good headspace.

The 762x54r headspaces on the rim, not the shoulder, btw.

what's a field guage then?  I see go, no-go and field.

Thank you very much swingset.  

If the bolt closes on a field gage you are supposed to reject it.  There's considerable disagreement on this.

Dennis Jenkins

Quoted: what's a field guage then?  I see go, no-go and field.

Quoted: If the bolt closes on a field gage you are supposed to reject it.  There's considerable disagreement on this. Dennis Jenkins Quoted: what's a field guage then?  I see go, no-go and field.

is it longer than a no-go gauge or is it in between the no-go and go gauges?

Quoted: Quoted: If the bolt closes on a field gage you are supposed to reject it.  There's considerable disagreement on this. Dennis Jenkins Quoted: what's a field guage then?  I see go, no-go and field. is it longer than a no-go gauge or is it in between the no-go and go gauges?

It's in between, closer to the "no-go" guage. It's supposed to tell you the gun is approaching "unsafe". The controversy comes from the fact that the standards used to measure headspace varies from commercial (SAAMI) and military standards. Generally, military standards are looser, for reliablity and long service life.....so a gun that measures "close to unsafe" on a SAAMI field guage might be completely fine.

The SMLE is a famous gun for this discrepancy. Nearly all Enfield .303 chambers measure close to "no go" by SAAMI specifications....and routinely fail "field" guages, yet are 100% safe to fire.

As for the Mosin-nagant. It is a rimmed cartridge and as such headspaces off the rim. Don't take this as gospel but I remember years back to place a piece of scotch tape on the bottom of a round and see if it will chamber. If it still chambers completely on the layers you are good to go, any more requires a more detailed analysis.
REMEMBER THIS IS A OLD MEMORY OF MINE AND AS SUCH MIGHT NOT BE QUITE RIGHT!
Use this info accordingly.

The field gage is longer than the nogo.

There's a short discussion of this on the Forster site.

Dennis Jenkins

Quoted: Quoted: If the bolt closes on a field gage you are supposed to reject it.  There's considerable disagreement on this. Dennis Jenkins Quoted: what's a field guage then?  I see go, no-go and field. is it longer than a no-go gauge or is it in between the no-go and go gauges?

Quoted: The field gage is longer than the nogo. There's a short discussion of this on the Forster site. Dennis Jenkins Quoted: Quoted: If the bolt closes on a field gage you are supposed to reject it.  There's considerable disagreement on this. Dennis Jenkins Quoted: what's a field guage then?  I see go, no-go and field. is it longer than a no-go gauge or is it in between the no-go and go gauges?

You're correct, I had it backwards....I don't use field guages so I was going on memory. Field is past "nogo" in length, to test the absolute maximum allowable safe headspace.

And if you reload you can go way past field if you gotta.

I don't do it though.

Dennis Jenkins

Quoted: Quoted: The field gage is longer than the nogo. There's a short discussion of this on the Forster site. Dennis Jenkins Quoted: Quoted: If the bolt closes on a field gage you are supposed to reject it.  There's considerable disagreement on this. Dennis Jenkins Quoted: what's a field guage then?  I see go, no-go and field. is it longer than a no-go gauge or is it in between the no-go and go gauges? You're correct, I had it backwards....I don't use field guages so I was going on memory. Field is past "nogo" in length, to test the absolute maximum allowable safe headspace.

Well, I've been really confused about the whole issue.  Every C&R rifle I get from online groups has a prominent tag that says I need to have the headspacing checked by a gunsmith before firing.  The cost of doing so would be prohibitive for me.  Also, I understand that the process requires removing the extractor from the bolt assembly and then using a specific gauge tool.  How could I possibly do that at a gun show? I can't imagine a vendor letting me dismantle all of his rifles for sale.  And online orders then sound like some kind of long distance roulette game.  I have recently obtained my C&R license and a few rifles and now I am a bit worried about ever shooting them.  Any advice would be much appreciated!    

A disclaimer saying you need to get your old rifle examined by a qualified gunsmith is just that.  It's meant to shift the liability burden to you.

Dennis Jenkins

Quoted: Well, I've been really confused about the whole issue.  Every C&R rifle I get from online groups has a prominent tag that says I need to have the headspacing checked by a gunsmith before firing.  The cost of doing so would be prohibitive for me.  Also, I understand that the process requires removing the extractor from the bolt assembly and then using a specific gauge tool.  How could I possibly do that at a gun show? I can't imagine a vendor letting me dismantle all of his rifles for sale.  And online orders then sound like some kind of long distance roulette game.  I have recently obtained my C&R license and a few rifles and now I am a bit worried about ever shooting them.  Any advice would be much appreciated!

So, has anyone ever heard of someone having a KB from a mil surplus rifle?  I'm a bit worried after seeing recommendations on what to fire and not fire in a recently acquired Spanish Guardia Cival mauser in .308 caliber.

There's all sorts of cautions involved in this stuff.  Shooting old guns is inherently dangerous activity.  People do it though.  Kind of nice if you know what's going on though.<G>

Dennis Jenkins

Quoted: So, has anyone ever heard of someone having a KB from a mil surplus rifle?  I'm a bit worried after seeing recommendations on what to fire and not fire in a recently acquired Spanish Guardia Cival mauser in .308 caliber.

Quoted: There's certainly nothing wrong with headspacing a surplus gun, and if you want the guages go to Midway or Brownells. Basically you have 2 guages which go into the chamber like a cartridge. They are marked "go" or minimum and "no-go" or maximum. The maximum guage is a guage that is too large, or would indicate that the headspace is excessive. The "minimum" is a the opposite, it indicates that the headspace is enough, but not too small. How they work is, you chamber the "go" guage, the bolt should close easily on it. Then, you chamber the "no-go" headspace guage. The bolt should NOT close on it. If it does, then the headspace is excessive. That's the short answer. That said, I have never nor will I ever headspace one. I put the gun on the bench, put a sandbag over the action, duck my head below the bench and fire the gun. Then, I see if the round is hard to extract, has any visible signs of cracking, pressure rings or pierced primers. If everything's cool, the case looks good, guess what? It's got good headspace. The 762x54r headspaces on the rim, not the shoulder, btw.

Sounds like the Army method of checking claymore wiring (sandbag in case the blasting cap goes off... outside the mine, of course)....

Quoted: Well, I've been really confused about the whole issue.  Every C&R rifle I get from online groups has a prominent tag that says I need to have the headspacing checked by a gunsmith before firing.  The cost of doing so would be prohibitive for me.  Also, I understand that the process requires removing the extractor from the bolt assembly and then using a specific gauge tool.  How could I possibly do that at a gun show? I can't imagine a vendor letting me dismantle all of his rifles for sale.  And online orders then sound like some kind of long distance roulette game.  I have recently obtained my C&R license and a few rifles and now I am a bit worried about ever shooting them.  Any advice would be much appreciated!

Just sandbag or remote fire (with your head below the bench) any new gun and check for pressure issues. Do this a few times, examine the brass, etc. If everything is cool, don't worry about it.

You shouldn't worry so much as to not enjoy your guns. Seriously, it's not that big of a deal if you just check it out and remote fire it.

Quoted: ...  And online orders then sound like some kind of long distance roulette game.  ...

Result of an unsuccessful spin of the Roulette wheel by me a couple of years ago with a mail order SMLE from AIM.

Left photo is a classic total head separation caused by excessive headspace (and lots of it!).

I sent the rifle back to AIM and they replaced it with a different one.



And just a reminder to always wear eye protection!!