M1 Garand headspace

[Bizio]

Dear Collectors,
I recently bought 3 Forster headspace gauges 30-06 and I checked headspace of my M1 Garand rifles.
One of them seems to have problem since with the NO-GO gauge the bolt lug is locking as it happens with the GO gauge.
With the FIELD gauge the bolt lug is almost locking and remains up of about 2 mm only.
Do you think is it still safe to shoot with this rifle ?
Before checking the headspace I shoot with this M1 Garand several ammo boxes, but now I am a bit afraid ...

Thank you.

---------- Post added at 07:58 AM ---------- Previous post was at 07:50 AM ----------

I forgot to tell that I also tryed on the same rifle other spare bolts I had but problem still remain, so I think or the chamber too large or the bolt tennons on receivers could be worn.

Information

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[Patrick Chadwick]

I would not have any worries at all. But I operate on a very simple principle - rifles shoot cartridges, not gauges. So I check the head clearance. This is something that I consider to be far more realistic for actual shooting than using gauges.

I have described the method several times in these forums, so please search for "head clearance" and save me the trouble of writing it all out again. Basically, it is a measurement of the REAL clearance or end play for a REAL cartridge case in the REAL rifle that you are REALLY going to shoot! All my rifles have been checked in this manner, and I do not possess a single headspace gauge.

Values obtained in this way are quite accurate enough to evaluate a rifle's suitability for shooting.
As far as safety is concerned, for semi-automatic rifles (Garand, .30MI carbine etc) a slightly too large clearance is no problem, all it does is stretch the cartridge case more than reloaders would like. But a real hazard would be a clearance of zero or even a negative clearance.

A negative clearance can arise with primers that protrude above the pocket, or cases that have been fired in another rifle with a slightly longer chamber and then not fully resized. Or cases fired again and again in the same rifle, so that the neck has streched so far that the case cannot chamber fully. Such overlong cases can cause a slam-fire, where the action of ramming the case into the chamber causes ignition of the primer, or out-of-battery-fire, where the bolt cannot quite fully lock-up - the situation that you observed with the field gauge. See Kuhnhausen, "The U.S..30 Caliber Gas Operated Carbines" for detailed descriptions of these similar (but not identical) faults, which are much more hazardous than stretching a piece of brass. And cannot be detected by headspace gauges, because the fault is in the cartridge!

That is the reason why cases for semi-automatics should normally be fully-sized - short cases may stretch the brass, but long cases are much worse! A generous clearance is safer than a negative clearance.

So enough theory, how about practice? A head clearance of 0.1-0.15mm (0.004-0.006") would be excellent. Up to 0.25mm (0.010") is usable, but above that, you are likely to see signs of stress in the cartridge case, about a centimeter above the base. I have one rifle that has a clearance of 0.4mm (0.016") and all it does is stretch the cases.

Personally, I would say your Garand is OK for everyday use. Not locking up on a field gauge seems correct to me. Others will disagree. But as already mentioned, my rifles fire cartridges, not headspace gauges.

[jmoore]

If it doesn't close fully with a field gage, then it is good to go back into the field! Brass life will suffer, but that wasn't a military concern.

[Bizio]

Thank you both for your answers.

[jmoore]

A quick additional note: The GO and No-Go gages were used as manufacturing limits. The field gage is a practical maximum. As the lugs are on a slight incline, "almost closed" is definitely not the same as "fully closed"!

[Orlando]

If lugs do not close on Field Gauge you are fine.
When checking headspace,make sure chamber is clean, bolt stripped, close bolt with light finger pressure only

[Bizio]

If lugs do not close on Field Gauge you are fine.
When checking headspace,make sure chamber is clean, bolt stripped, close bolt with light finger pressure only

Thanks, I had follow instructions here.
Inspecting your M1 Garand