I want to make sure headspace on a 30-06 rifle is safe and within limits.

Since I have no access to go, nongo and fieldgauges and they are very difficult to get here, I followed the advice of a man who owns a gunrepair shop who told me he has used this method for years when he has to judge a rifle for which he has no gauges.

I took 5 factory cartrides of a well known brand, gently pulled off the bullets,removed the powder and primers. Then I trimmed the cases to exact equal lenght, measured them with a caliper and found tolerances to be within .0004. After that I reset new primers only partially, so that they are well above the casehead. I then gently chambered these cases in the rifle with a fully disassembled bold. Then I measured them again and found headspace differing from .00740-.00748.
I then checked these data with specifications I found on the site of a gauge manufacturor. These people state that that tolerance between their go and non-go is .006 and .009 between their go and their field. This would mean this rifle has excessive headspace.

On another site I read a technical note by Armalite on headspace, from which I quote:

************************

" Headspace ranges are established by industry advisory bodies, government bodies, or by individual manufacturers. In the U.S. the primary advisory body is the Small Arms and Ammunition Manufacturers Institute (SAMMI). Issues of producibility, safety, and mechanism reliability with a particular cartridge must be considered. Firearm manufacturers must produce firearms with chamber headspace that is producible, yet assures safe and reliable operation with all ammunition made to standard. This becomes an extremely difficult challenge when making self-loading firearms.

EXAMPLE: A .308 Winchester rifle with a SAAMI chamber, and ammunition made to SAAMI standard cartridge dimensions and tolerances reveals acceptable headspace ranges of:

Chamber dimensions: 1.630 minimum to 1.640 maximum
Minus case dimensions:1.634 maximum to 1.627 minimum
Resulting headspace: .004 interference to.013 clearance

In this example, the SAAMI maximum headspace/minimum cartridge allowance produces so much clearance, .013 inch, that it will reduce case life. This much headspace would probably be found only on a used rifle. The SAAMI minimum headspace/maximum case condition produces .004 inch of interference that could make semi-automatic operation unreliable. The challenge for a manufacturer is to find a headspace range large enough to allow reliable operation and small enough to assure accuracy by aligning the cartridge in the chamber uniformly. Dimensions for new firearms should be equal to or larger"

**************************

The headspace I found is excessive compared to Saami specifications, but well within the maximum clearance of .013 as stated above.

Now I am puzzled and would like three questions to be answered:

1. Is this way of actually measuring headspace safe, compared to the static measures of the gauges?

2. Is the amount of headspace I measured beyond safe limits
and the rifle therefor unsafe to fire?

3. If the rifle is not to be declared unsafe, and if I fired safe loads using new brass, then determine that there is no sign of case head separation or other failure whatsoever, partially necksize these cases and reload them again, would I have solved the problem of excessive headspace?

Would I not be doing the same as those people who develop wildcats and fireform their cartrides from the original calibre on which their wildcat is based?

You are NOT measuring headspace (with your methiod), instead your measuring clearance. Headspace is minimum (0) to + .006 as measured from the boltface to the datum point on the chamber shoulder cut. Cartridges normaly run -.002 to-.010 to the same point on the shoulder (rifle bolts make lousy sizing dies).
Note: DATUM POINT ON THE SHOULDER.

Shoot it just like it is, when you reload the cartridges set your sizing die to only push the shoulders back .001-.002 (partial FL size).
Of course I also question the precision of your caliper measurments, as no machinest worth there salt would trust a caliper to .001, let alone attempt to read it to 10 millionths of a inch (.00001)

Quote:

---

.00740-.00748.

---

Tailgunner is right. The question sometimes comes up about a belted mag rifle with too generous shoulder room.When reloading these and in your case, you size the case to your chamber , whatever that may be