head spacing....

[ave8er]

In the interest of safety and under the advise of people who know way more than me, I took my rifle to a gunsmith to have the headspacing checked. He took the rifle in the back came back and said it was fine.... I expected a little more, like maybe an actual number? Something like " sir you head space is 2.5 thousandths..." I am not sure he really checked it... Can some one tell me what is actually involved in this process. I guess I should have asked to watch? On a positive note, it was free.

Information

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[browningautorifle]

It's just a stainless gauge that resembles a cartridge. There's a proceedure to it but that's all it is. I'm sure someone will be here in a minute to spell it out but it only takes a few minutes. There's a go, a no go and for military rifles a field gauge. The actual measurements are built into the gauge.

[emmagee1917]

Briefly , the short gauge is a "go" , your gun should close on this. This means that any round in spec will chamber safely in your gun without binding up. The next longest is the "no-go" . If your gun is new or just rebarreled it should not close om this one. If it does , someone screwed up and you have been robbed of some of your guns life span. As the gun is used and wear sets in , it will close on the no-go. This is when the longest gauge , the "field" gauge , comes into play. When the rifle will close on the field gauge , it means it's life is about shot or has passed. At this point it needs attention , rebarreled , a new bolt fitted , whatever.
Depending on your rifle and the brand/type of gauge , this check could be as simple as cleaning the chamber and dropping the gauge in like a round , or you may have to strip the bolt down. As was said , it usually does not take long and most smiths will have the popular ones for thier area there.
HTH , Chris

[Sunray]

Hi. Headspace guages don't measure anything or produce a number. They just tell you if the headspace is within tolerance.

[browningautorifle]

Headspace guages don't measure anything

Sure they have a measurement. They are a certain length. This is built into them. If you can't be more helpful than this don't cloud the issue.

[Jim Tarleton]

Sure they have a measurement. They are a certain length. This is built into them. If you can't be more helpful than this don't cloud the issue.

I believe that Sunray was just trying to point out that no actual measurement of headspace is generated, or put another way, no definitive value of headspace is known. One only knows that the headspace measurement is between two values represented by the two gauges, or in the extreme case of FIELD or GO failure, exceeds or is less than a particular headspace measurement.

As simple as a headspace check is, many do it incorrectly. There is an excellent description of the process in Hatcher's Notebook.

Jim

[firstflabn]

Hi Jim, some struggle a bit with the concept. Understandable when you're dealing with a dimension almost too small to see and is obstructed so you can't see it anyway. Your description should help. I point out that in a general sense my foot is a go gauge when I try on a new pair of shoes - doesn't tell me the exact measurement inside the shoe, but it does tell me if the shoe is at least long enough. Harder to come up with an everyday example for the no-go.

Now, try to explain to non-reloaders why all this go, no-go talk relies on the assumption that case length is within spec. (pet peeve of mine).

[RCS]

Here are the numbers that I recall: minimum or short is 1.940, most rifles from the factory are 1.942 or 1.943, 1.945 is no-go and field gage is 1.950

[Jim Tarleton]

Here are the numbers that I recall: minimum or short is 1.940, most rifles from the factory are 1.942 or 1.943, 1.945 is no-go and field gage is 1.950

Using your values, there is only 0.010" difference between a GO and a Field, but there is a total tolerance of 0.012" for the manufactured round (0.006" too short to 0.006" too long) from the standard. If your reloading dies have 14 TPI, that is 0.0714" per revolution. 1/7th of a revolution of the die spans the entire range of the gages (51.4 degrees). There is only 0.005" between a GO and a NOGO, or 1/14th of a revolution of the die (25.7 degrees). I firmly believe that many concerns over headspace are unwarranted, and should be non-existent if one reloads for that particular rifle. In my experience, neck sizing leads to over-length rounds that require some degree of extra bolt force to chamber if you are firing 45,000 psi or greater loads.

Let's say your actual headspace is 0.1.944", which is within tolerance of the NOGO. You chamber a round that is 1.936", also within tolerance of round. The difference is 0.008" (the approximate diameter of the thickest human hair), which is barely within tolerance of the FIELD, and significantly exceeds the NOGO tolerance of 0.005". If your chamber is 1.949, within tolerance of a FIELD, and you chamber the same 1.936" round, again within tolerance. The difference of 0.016" exceeds the total range between a GO and FIELD of 0.010" by 160%, even though the rifle was within FIELD tolerance. This brings us back to firstflabn's comment. In other words, one should also consider the ammunition used when evaluating problems. Unfortunately, those gages aren't commonly available, and we still must rely on headspace gages.

The diameter of a human hair varies from 0.00067" to 0.0071", just to give one some idea of the degree of tolerance of which we speak.

Any errors in this post are entirely the fault of my 5th grade math teacher.

Jim

[ave8er]

Yeah, you went about 5 miles + .005 over my head with all that. I full length re-size everything I re-load. I screw the die down till it touches the shell holder and then back it off about the thickness of a piece of paper, so about .003. I do use case gauges for rifle rounds. They are a go/no go kind of affair...