Head spacing with only a FIELD gauge.

[tenOC]

Ten, are they also stamped with those same numbers? I guess mine are older than I thought - without pulling them out, I remember them as 1.290, 1.296, and 1.302. - Bob

"...only use the FIELD gauge..." That doesn't actually check the headspace. It only tell you the thing is at less than max.
Yours closing on the No-Go but not the Field indicates it's safe to shoot, but is close to max.
"...My Forster Field does measure..." Headspace gauges do not 'measure' anything. They only tell you if the thing is within tolerance or not.
Graf's shows the Forster No-Go gauge to be 1.296". Not that it matters. They don't list the other 2 gauges.

They're actually stamped 1.290, 1.296 and 1.299, but I measured them with a digi micrometer made in the largest Asian nation and sold at a premium from a very high end tool distributor outlet called Harbor Freight. So....there ya go. China is always right, aren't they?

Information

Warning: This is a relatively older thread This discussion is older than 360 days. Some information contained in it may no longer be current.

[USGI]

They're actually stamped 1.290, 1.296 and 1.299.

Mine are the same, I should have checked before posting - they weren't buried as deep in my Carbine "stuff" as I thought they were! - Bob

[Patrick Chadwick]

So....there ya go. China is always right, aren't they?

This is an oldie:

The fact that an instrument has a resolution of 0.001" does NOT mean that it is accurate to 0.001".

The slightest bit of grease or dust on the faces of a gauge will affect the reading. As will the temperature. Or the slightest skew of the object being measured. If you are really concerned about accuracy, then you need a reference bar. In high-quality micrometer cases there used to be an hook spanner and a 1" reference bar for adjustment. I am lucky enough to possess a cased 2" bench micrometer that reads to 0.0001". The reference bars have plastic grips for a very good reason - with the bench micrometer you start to detect the difference between a "cold" measurement - i.e. out of the cupboard - and "hot" - i.e. after you have held the object in your hands for a while.

So while your digital gauge may be readable to a resolution of .001", do not trust it blindly. At best it is indicating that a measurement of, say, 1.296" is closer to 1.296" than 1.295" or 1.297" provided that all parts are spotlessly clean and at the same moderate temperature.

[tenOC]

Yeah. Thanks for teaching me about grease and skewing an object.

[Bubba-7]

TM 9-1276 February 1953, page 14
1.290
1.295
1.298
1.302
Page 37 for usage of each gauge.

[painter777]

Headspace gauges do not 'measure' anything. They only tell you if the thing is within tolerance or not.

A Head Space Guage is used for measurement.

1.290"
1.295"
1.300"
Above are the USGI examples I used from TM9-1276_1947
Head space is MEASURED with a set of GO,NO-GO and FIELD guages.

Maybe a definition of Head Space (In Firearms) may be required here:

Head Space is the distance measured from the part of the chamber that stops forward motion of the cartridge (the datum reference) to the face of the bolt.

These Head Space Guages were required by US armorers to be sent yearly in to a Arsenal to be Inspected. Above from TM9-1276_1947 page 18, in section 15 part 4 under Note.
Must have been for Inspection and Calibration of Length and Diameter.

You still think they were used for 'Close Enough' type calculations. Like your only a 1/3 of a quart of oil low ?

[painter777]

TM9-1276_1947
http://www.90thidpg.us/Reference/Man...-1276_1947.pdf

Shows 1.290 (GO), 1.295 and 1.300 (NO GO) ... page 25.

Section 15 on pages 17-18 reads:
15. Headspace Gauging
a. The headspace of a carbine is the distance between the shoulder
of the chamber and the face of the bolt when the bolt is in locked position. If headspace is insufficient, the bolt will not fully lock behind the
cartridge without being forced. If headspace is excessive, the cartridge
will have too much play in the chamber when the bolt is locked behind it.
Either condition is unsafe. As component parts of the carbine
are manufactured to close tolerances and headspace is carefully checked
at manufacture, a variation usually is due to wear and causes excessive
headspace to develop. However, assembly of parts with maximum
tolerances may result in either excessive or insufficient headspace.
b. Excessive headspace due to wear may be caused by advanced
chamber shoulder, worn faces of bolt, worn locking lugs on bolt, or
worn locking shoulders in the receiver.
c. Test headspace with gauge (fig: 54), as follows:
(1) Clean bore, chamber of barrel, and operating parts thoroughly,
wipe dry, and inspect for metal fouling or foreign matter. Operate
the mechanism a few times to see that bolt closes and locks smoothly
on an empty chamber.
(2) Retract and hang the bolt by means of the slide stop. Place the
headspace gauge on the face of the bolt, gripped by the extractor. Be
sure that gauge is perfectly clean and dry.
(3) Retract the bolt slightly to disengage the operating slide stop,
and allow the bolt to move slowly forward to the locked position so
the gauge enters the chamber of the barrel. If the bolt locks fully on
the maximum gauge, the headspace is excessive and the carbine unserviceable. Lock the bolt completely when the minimum gauge is used.
Caution: Do not force, or allow bolt to close sharply under spring
propulsion.
(4) Pull back bolt and remove gauge.
Note. See serviceability chart (fig. 19) for proper headspace gauge. Forward headspace gauges to an arsenal once a year for checking.

After Re-barreling, For Proper Headspace... page 79/80..

CHECKING CHAMBER FOR PROPER HEADSPACE. If after rebarreling, there is insufficient headspace indicated by the bolt failing to close on the 1.290 headspace gauge (41-G-199-175), the chamber must be reamed with carbine reamer (41-R-488-125).
To correct insufficient headspace, proceed in the following manner:
(1) Dip reamer in lard oil and place in chamber through top opening of receiver. (See fig. 55.) Turning handle slowly to the right, remove only sufficient metal to permit bolt to close on 1.290-inch headspace gauge (41-G-199-175).
(2) Wash chips from reamer with lard oil after removing from
chamber.
(3) Handle reamer with care to prevent it from being chipped or
nicked. Never turn reamer backwards in chamber, as this tends to
dull the cutting edges.
(4) If bolt closes properly on the GO gauge (1.290), the NO GO
gauge 1.300 (41-G-199-200) is then inserted. The bolt should not
close on the 1.300 gauge. If bolt does lock completely, it indicates too
much headspace. In this case, use a maximum bolt and try the gauge
again. If this bolt also locks completely, the receiver is not usable.

[Al Diehl]

Here at work we do services on military rifles (M4A1s) and MGs (M249s and M240s) week in and week out. We only use the "Field" gage.

When I am at home, I use both the Go and No-Go gages. If it fails No-Go I don't see any reason to take a chance on shooting it.

Al