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Posted: 1/26/2011 4:51:12 PM EDT
So I think there might be a headspacing issue on my m1a. Now of the 3 sources I have gone too, 2 of them said the headspacing was excessive the third said it was fine. The first too simply took the. 308 go/no-go gauges and tried them in the rifle. The third disassembled the bolt before checking with the gauges. Which method is correct? Im think that if the bolt will close on the no go while assembled than it should for sure close when disassembled. I tried to google the correct method but came up with nothing.

Link Posted: 1/26/2011 6:30:36 PM EDT
3rd guy was right.
Quick and dirty guide for you.......

1-Clean the chamber and bolt very well. Don't want gunk to throw off readings.
2-Strip the bolt of the ejector and extractor. Most gauges do not have a cut out at the base to allow accurate reading when checking the headspace. This allows the rear of the gauge to rest fully against the bolt face.
3-Using only finger pressure (op rod spring was removed) try to close the bolt on the gauges.

The .308 vs. 7.62x51 headspace can be slightly different. A .308 has tighter dimentions and the 7.62 is more loose (military reliability).

Bolt should rotate closed on "Go" gauge, may close on "No-Go" (thats getting long in headspace for .308), must not close on "Field Reject" (headspace is long and needs adjustment)
Link Posted: 1/26/2011 7:28:16 PM EDT
[Last Edit: 1/26/2011 7:31:29 PM EDT by SteelonSteel]
the two most common gage brands are Forster and Clymer. Clymer has a rep for tightly adhering to the standards. Forster gages reportedly tend to wander from spec.

sooo if one smith used one brand and the other guy used another you could get different results.

-also some gages came with cut outs to use in the m1/m14 so you didn't have disassemble the bolt. Personally I would disassemble the bolt. If the cut wasn't there and the smith didn't strip the bolt then the readings were bullshit as the ejector was pushing damn hard on the gage to get any reliable reading. Op rod and spring out, bolt stripped, insert gage into spotless chamber and gently finger close the bolt on the gage. If the right lug is up any amount above the reciever than it does not close on that gage.

-like was mentioned before the saami min and max don't match up with the military min and max. IIRC the mil min is just under the civi max. IIRC civi 1.630 - 1.634 or 5. mil was 1.633 to 1.638 ish. and the mil national match was different than either of those. Those numbers are off the top of my head and I guess they merely show the relationship of civi to mil.

I always figured ideal was 1.633 headspace, just right for civi and mil cartridges with a good safety margin.
Link Posted: 1/26/2011 8:26:32 PM EDT
Good info and thank you for the replies.

Link Posted: 1/29/2011 9:22:06 PM EDT
I like 1.634" which is low end of commercial no go and spot on for NATO
Only way to know for sure is to have a set of commercial dimension .308 gages and a set of NATO dimension 7.62X51
I have a full set of gages that go from 1.630" to 1.638" plus a USGI 1.640" field gage.

Forster gages are well dimensioned, the problem is that they do require you to remove the firing pin & extractor/ejector assemblies to gain an accurate read.
If the gages are wandering it is because the users are not doing this.

I have always held the opinion the most accurate read is gained with the component parts removed from the breechface of all weapons being checked.
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