Military vs, SAAMI headspace spec?

[jacobhh]

How much more lenient are Military headspace specs than SAMMI?
Will a milsurp fail a SAMMI Field spec test and still pass a military
NoGo check?

I'm particularly interested in the US model 1917 headspace. I've
read that these rifles were rushed produced due to need and
initially 1/3 failed headspace from the factory. Did the military
loosen the spec. to get these much needed rifles into the field,
and by how much?

In my limited experience I have yet to come across an 03 or 03A3
offered for sale that fails my Forster Field gauge yet two 1917's
have and one the owner claimed was directly from CMP.

I won't shoot a gun that fails a SAMII Field test regardless of
what heavy military case or extra strong action is purportedly
used. I've seen some pretty rough looking Lake City brass used
for reloads. If not for safety than at least I'd like to use my brass
more than once.

Any other opinions out there?

 

[DMK]

That depends on the caliber.

While the specs for NATO 7.62x51 are slightly different than commercial SAAMI specs for .308 (difference in specs here), I don't know of any differences between military 30-06 and commercial 30-06.

It's my understanding that a rifle should pass a no-go test for best performance. A rifle failing a no-go test, but passing a field test is still safe and serviceable, but not optimal. A rifle failing a field test is unsafe to fire.

You just have to make sure you are using the correct headspace gauges.

For example, with 308/7.62x51: If you plan to shoot .308, you need to use a set of .308 headspace gauges. If you plan to shoot 7.62x51, a .308 go(1.630")/no-go(1.634") test might be a little tight for some 7.62x51 ammo. (I headspaced my FALs and 7.62x51 chamberd Garand at just under SAAMI no-go so I can shoot both .308 and 7.62x51)

However, 30-06 doesn't have a NATO spec. I know of only SAAMI headspace gauges for it. If your rifle does not pass the field gauge test, then it is unsafe to fire and probably needs a new bolt or to have the barrel setback and rechambered.

I have yet to come across an 03 or 03A3
offered for sale that fails my Forster Field gauge yet two 1917's
have and one the owner claimed was directly from CMP.

You might want to post in the Ask Orest forum at ODCMP's forums and see how these tested when they headspaced them.

http://www.odcmp.org/new_forum/forum.asp?FORUM_ID=27

I've read that these rifles were rushed produced due to need and
initially 1/3 failed headspace from the factory. Did the military
loosen the spec. to get these much needed rifles into the field,
and by how much?

I wouldn't doubt that. Don't forget that the military also continued to issue low serial numbered M1903s even after they were determined to have bad heat treating. However, it is definitely not recommended to shoot one as a civilian. Uncle Sam does what's best for Uncle Sam, not what's best for the men in the field.

 

[Art Eatman]

If I had a 1917 that failed the field test--or, maybe, even the NoGo test--I'd just have the barrel set back one thread. No big deal.

Re the low-number Springfields: My understanding is that the military loads were at some 47,000 psi, and the rifles didn't fail at that pressure. Breakage came about from other testing; after they determined the cause, the rifles were withdrawn. I got into '06s and handloading in 1950, and the low-number thing was ancient history at that time. I know that Phil Sharpe commented on it in the 1930s, but he was repeating common knowledge.

Art

 

[Jim Watson]

Hatcher's Notebook describes a case of 1917s claimed to have excess headspace. Turned out the guy did not know how to use a headspace gauge and all the rifles were fine.

Hatcher also covered the "low number" Springfield pretty thoroughly.

 

[jacobhh]

Jim,
I've heard that. Please explain how one would improperly close a bolt on a Field gauge
without forcing it?
Thanks

 

[Jim Watson]

That's the point, the guy Hatcher talked about WAS forcing it. Headspace is properly checked with the bolt stripped and pinkie pressure on the handle. I don't know about the 1917s you saw but the ones Hatcher checked were fine.

 

[jacobhh]

I understand you Jim and appreciate the explanation.
What your telling me is that less pressure must be
used to check headspace on a 1917 than is required to
cock the firing pin. That, IMHO, smells suspiciously
like Government specification/contractor voodoo.
I believe, however that you've told me the facts of the
case. And I agree that you have outlined the correct
way to check headspace.

I have a picture in my mind of the contractor demonstrating
to the Government armorer how to close the bolt with his
pinkie subsequent to the armorer indelicately closing the
bolt on a Field gauge.

*The above remarks are only the opinion of the individual and
should not be construed to reflect the views of any Gunsmith,
Engineering School, Test Engineering Organization, Contractor or
Sovereign Government.*

 

[DMK]

Headspace gauges are designed to be used with minimal pressure to measure the specified clearance. You do not want to force the bolt closed. The rifle's bolt gives you an appreciable amount of mechanical leverage and will crush the gauge slightly, giving a false reading. We are talking about differences of only one hundredths of an inch here.

The same reasoning goes with using calipers. You only want just enough pressure to touch the object being measured. Otherwise you may be distorting the material or flexing the instrument, again giving a false reading.

 

[Jim Watson]

I think headspace measurement is overemphasized on the Internet. I do not recall an account of anybody having casehead separation or other trouble from a surplus gun with a little excess chamber headspace but otherwise in good condition firing good quality surplus or commercial ammunition.

A reloader who screwed the sizing die down hard against the shellholder would run into trouble before long, but that just means he should learn how to adjust his dies to keep fireformed brass to chamber spec instead of die spec.

 

[jacobhh]

OK, please bear with me on this one.

Setting aside the 03 and 1917 in .30-06 for a moment.
I pick up my 8mm Mauser gauges. I have two
of those. One is a '98 RC mixmaster, the other
a two war two generation Turk. The gauges are:
GO- 1.8743 Forster
NOGO- 1.8803 Forster
FIELD- 1.8843 Forster
I notice Forster has gone to the expense of machining
a rimless head in the gauge with through hole in base
matching the 8mm cartridge spec. The gauges are of
.0001 resolution and.001 accuracy as per NBS convention.

In flagrant disregard for proper 'Qualified Gunsmith' procedure.
I carefully clip the GO gauge under the extractor and operating
the bolt I guide the gauge into the chamber it slides in with NO
discernable resistance like a ball bearing down a rainspout.
Repeating with the NOGO gauge I encounter resistance and do
not completely close the bolt. The field gauge resists and I stop
sooner feeling I couldn't force this baby if I beat on the handle
with a hammer. Same results with the Turk and using .30-06
gauges in my very good conditon 03A3. I try it on a 1917 I'm
considering with a $995.00 sticker (a Winchester-sub contract,
no W's on the parts). NO discernable resistance to the field gauge!
The gauge slides in and the bolt closes as if P.O.Ackley himself
machined the chamber to a Forster .30-06 Field gauge. I don't
care how they machined the Cam, that rifle is bogus! And as far
as .01 inch compression I would expect that kind of inaccuracy
from the nib end of a 3rd grader's plastic ruler after he autographed
the sidewalk with it but not from a precision machined gauge of hard
carbon steel placed against a military .30-06 rifle chamber. Just my,
possibly worthless, opinion. Your call.

Jim as far as 'overemphasized.' I tend to agree, but when dropping
$1000 bucks, I like the reassurance. I do fireform my brass and
believe it's a good idea.

 

[30Cal]

The No-Go gage is only used when rebarrelling the rifle and it's used to give assurance that the headspace will be good for most if not the complete life of the barrel. If it's not a new barrel, use the Field gage.

 

[Jim Watson]

Well, I guess you found a dud Winchester, then. Or maybe a reasonable imitation of one, eh? I didn't know the minutae of 1917 production had jacked up prices for oddballs. Sorry 'bout that.