Headspace soul-searching: 308 vs 7.62 NATO

I have a Spanish FR8 (large-ring Mauser action), which I purchased as a general purpose hunting/plinking rifle. I've fired all manner of surplus and commercial ammo through it, to include my various reloads, and not had any issues, save some minor sticking of the bolt with one particular lot of German surplus 7.62x51. Nevertheless, I decided to purchase a .308 Winchester field gauge. Now I was/am aware of the dimensional difference between NATO and commercial chambers, but there is an overlap, and if it passed a commercial field gauge, then it would obviously pass a NATO max chamber gauge. Alas, the bolt closed easily upon my new Forster gauge. I now have a NATO gauge on the way. So, here's my dilemma:

If the rifle passes the NATO Max gauge, do I really need to stop shooting all commercial ammo? Or is that all made to the same specs anyway?

If she fails the Max gauge, what would be my best option in regards to having the headspace fixed? The neck-size-only method is not acceptable, as I like to use this thing as my 30-caliber garbage disposal. For reference, the 308 Field gauge is 1.638", and the NATO Max gauge will be 1.6455".

If both types of ammo work--- I'd just keep doing what you're doing.

My understanding is: The cases are made to the same specs. and like everything else-- they have a tolerance factor.
The military chamber is a little more on the 'generous' side to be sure and easily accept any and all ammo even if might
be somewhat dirty, a little long or short, and/or on the larger side of the case tolerances.

Your bolt sticking might have been due to the pressure level of that ammo batch more than
something going on with case dimensions.
If one batch of ammo is giving problems--- I'd look there first. Everything else is probably OK.

Are there any actual issues with your rifle? Or why did you decide to purchase the head space gauge?

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Originally Posted by cwtebay

Are there any actual issues with your rifle? Or why did you decide to purchase the head space gauge?

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Mostly because I had never bothered to check it, and this has rapidly become my favorite bolt-action rifle, so I shoot it quite a bit (I will eventually send a few thousand rounds down-range, at this rate). But some of my German surplus is a little difficult to extract, so it has been nagging at the back of my mind for a while.

Keep shooting. If you reload for that rifle either neck size only or minimally full size. Most factory dies will take to minimal dimension if you bump the shellholder.
Rick

The NATO chamber is mainly designed for reliability under sustained operation. Think select fire weapons. That’s why the dimensions are generous, because metal expands under heat.

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Originally Posted by zarrinvz24

The NATO chamber is mainly designed for reliability under sustained operation. Think select fire weapons. That’s why the dimensions are generous, because metal expands under heat.

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Dirty high volume shooting is the reason for the generous chamber. As the chamber gets hot it expands so it becomes larger not smaller.

To the OP brass life and a possible head separation is would be your possible issues. Unless the headspace is truly excessive head separations on new brass should not be an issue. That being said make sure you are wearing shooting glasses.

Well, since I haven't had any reloaded case heads separate, it must not be too bad. As long as it doesn't close on the NATO gauge, the matter seems to be settled. I appreciate all the input.

As a hand loader, head space should never be an issue. We tailor the cartridge to the chamber.

The Germans especially used to be known for loooong headspace measurements -- no go often went in on Mausers. They considered it a safe practice anyway (if memory serves, they'd even allow .010! (somebody correct me if I'm wrong). The current NATO 308/7.62 field gauge is almost that long. Your cases are shorter, but still, if it were mine and I had no trouble to this point, I wouldn't worry too much re shooting new ammo in it. However: After that, minimally size the cases (which is a good idea anyway unless multiple guns are involved) and watch for case-separation rings to form near the head. Split case events are not a good thing.

Hopefully that "stickiness" is not lug set back, which also can cause excessively long headspace.

Even though the FR8 is based on a M98 action, it is (inferior(?)) Spanish steel and possibly intended for 7.62 CETME, not NATO or 308 ammo.

That being said, I never had any stickyness or headspace problems shooting a steady diet of 7.62 NATO in my FR8.

First off I would not trust a Forster gauge. I set up a rifle using one and it would not chamber a factory round. Talked to Dave at pacific tool and he told me that their gauges are not alway accurate. Military ammo is usually loaded a bit hotter than commercial ammo and the military guns usually have a little more free bore than commercial rifles. Some Mausers do have a problem with bolt set back in the frame. The military actions were designed for the 8X57 which is lower pressure than a 308. This makes it difficult to rase the bolt handle after firing because the bolt has to move forward a small amount and the fired brass will not let it.

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Originally Posted by waksupi

As a hand loader, head space should never be an issue. We tailor the cartridge to the chamber.

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There you go.

If we simply strive to duplicate factory specification ammo we give up much of what handloading offers. I've never given a red-hot-happy what my firearm's headspace may be.

The thing to check for is case stretch just above the rim.

Forster gages have been known to be off. I remember reading an anecdotal story on the M14 forum where the writer was in charge of a USMC depot, maybe even the shooting team one at the time. They gage their gages as quality control. Forster was all over the place. Clymer were very close to spec and after that spot check is all they would procure. The Forster gages were disposed of as useless.

I buy Clymer gages.

"Even though the FR8 is based on a M98 action, it is (inferior(?)) Spanish steel and possibly intended for 7.62 CETME, not NATO or 308 ammo."

In the case of 7.62 NATO M80 Ball the transducer MAP is 62,000 psi. However, most M80 Ball I have tested runs 54,000 t0 60,000 psi(M43). Tested commercial .308W runs from 54,000 to 61,000 psi(M43). The MAP for the .308W is 62,000 psi (transducer/strain gauge).

As to 7.62 CETME ammunition, it is the common statement that it is “lower powered ammunition loaded for the FR7/FR8 rifles”. Such is simply not true. The 7.62 CETME ammunition was loaded to ensure reliable functioning in CETME rifles pre fluted chamber. They used a lighter weight bullet and a faster burning powder to make the time/pressure curve quicker. That let the case contract prior to the extraction cycle starting. The measured psi(M43) of 1962 CETME ammunition produced in Spain runs 58,000 to 60,000 psi. Not exactly a reduced load.

Attachment 285392
Attachment 285393

If you hable Española from the horses mouth regarding FR7 and FR's.....made for 7.62 NATO ammunition and compatible with 7.62 CETME spec ammunition.

Attachment 285394
Attachment 285395
Attachment 285396
Attachment 285397

As to the headspace being "generous", the FR8 is a CRF Mauser M98 action which was made for use with German level 8x57 loads and converted to 7.62 NATO. Being a CRF action the case is held to the bolt face by the extractor regardless of the headspace dimension of the shoulder dimension. The case will fire form on firing w/o any problems. Simply size FL the case so the shoulder isn't excessively set back or just neck size for long case life.

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Originally Posted by waksupi

As a hand loader, head space should never be an issue. We tailor the cartridge to the chamber.

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Yep, not even concerned with it. I have plenty of .308 brass and if it stretches a bit on the first firing, so be it.

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Originally Posted by HumptyDumpty

Well, since I haven't had any reloaded case heads separate, it must not be too bad. As long as it doesn't close on the NATO gauge, the matter seems to be settled. I appreciate all the input.

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Back in the '90's I bought an FR-8 out of Gun List for somewhere around $150 and converted it to a sweet Scout Rifle. I've carried that rifle more than any other I own and have probably killed more game with it than any other I own. My oldest daughter used it and cast loads to kill her first couple of deer when she was a teenager. It never occurred to me to check the headspace.

My mama used to tell me "Don't borrow trouble." I think that applies here. Just shoot and be happy.

35W

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Originally Posted by John Taylor

First off I would not trust a Forster gauge. I set up a rifle using one and it would not chamber a factory round. Talked to Dave at pacific tool and he told me that their gauges are not alway accurate. Military ammo is usually loaded a bit hotter than commercial ammo and the military guns usually have a little more free bore than commercial rifles. Some Mausers do have a problem with bolt set back in the frame. The military actions were designed for the 8X57 which is lower pressure than a 308. This makes it difficult to rase the bolt handle after firing because the bolt has to move forward a small amount and the fired brass will not let it.

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One issue with Forster gages is the way they take their measurements. They do it differently than the way that Clymer and some others do. Clymer and Manson gages tend to be more technically accurate to Ordnance drawings of military cartridges.

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Originally Posted by Lance Boyle

Forster gages have been known to be off. I remember reading an anecdotal story on the M14 forum where the writer was in charge of a USMC depot, maybe even the shooting team one at the time. They gage their gages as quality control. Forster was all over the place. Clymer were very close to spec and after that spot check is all they would procure. The Forster gages were disposed of as useless.

I buy Clymer gages.

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The gentleman that you refer to is 'Gus' Fisher, retired NCOIC of the USMC Precision Weapons section at Quantico. The thread referenced is located here:

https://www.m14forum.com/threads/a-l...adspace.66601/

Here is a thread from the FAL Files where a member took measurements of an assortment of then readily available ammo. You may be surprised how 'short' some ammo actually is:

https://www.falfiles.com/threads/amm.../#post-3025389


To the OP: if I were in your shoes and I was concerned about excessive headspace, I think I would seriously consider locating a good, dependable gunsmith, and have my barrel set back 1-2 threads and rechambered - or simply replaced.

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Originally Posted by nicholst55

One issue with Forster gages is the way they take their measurements. They do it differently than the way that Clymer and some others do. Clymer and Manson gages tend to be more technically accurate to Ordnance drawings of military cartridges.

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That is not correct regardless of what Gus claims.

Most if not all US manufacture use the U.S. Sporting Arms and Ammunition Manufacturers’ Institute (SAAMI) spec'ed chambers and gauges. They can be found here. https://saami.org/technical-informat...ami-standards/

Permanent International Commission for Firearms Testing – commonly abbreviated as C.I.P. or CIP is the European Equivalent of SAAMI but there are differences. https://www.thefirearmblog.com/blog/...ivalent-saami/

The third is the NATO—EPVAT (Electronic Pressure Velocity and Action Time) firearm regulatory organization. They seem to align more with CIP than SAAMI. The 5.56 and 7.62 x 51 will conform to this standard. The 308 Win and the .223 Rem will conform to SAAMI standards.

Forster gauges are purchased either as SAAMI or NATO. If they do not meet the tolerances that is a QC issue. https://www.forsterproducts.com/prod...adspace-gages/

Before I retired I would inspect all my gauges and reamers on a 100X optical comparator and I did find some GC issues with some other brands, however, out of the 2 dozen or so Forster I have not found any out of spec. That includes the Forster gauges that were used on team firearms and yes they had to be calibrated through the PMEL lab (Precision Measurement Equipment Laboratory (PMEL) is a United States Air Force (USAF) facility in which the calibration and repair of test equipment is accomplished).

I have the Forster .001" step sets in .223, 308 and 30/06 plus miscellaneous other go/no go gauges in other calibers.

On a side note in 25 plus years of having PMEL do the initial calibration of precision inspection equipment like gage blocks, indicators and mics. the percentage of fails was surprising high. It took me 3 sets before I had a serviceable set of Starrett Webber gage blocks.