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Posted: 3/4/2006 8:31:15 AM EDT
I've seen more on headspace lately than in recent years. It seems to go in cycles. Maybe some new writers think they have something to add onto what is really a totally misunderstood item.

Nobody seems to mention that the gauge, bolt and chamber must be SQUEAKY clean before you try to "measure" the headspace.

Nobody even seems to mention that using a headspace gauge, like using a micrometer, requires a certain feel or touch by the person doing the job, and that an extremely light touch is needed.

Let me give you two examples of what I've seen. I certain gunsmith, who was ok at doing basic repair, decided one day to accept the job doing the final reaming on what was going to be a match chamber, to be cut with minimum gauged size. He cut, "gauged", cut, "gauged", cut... until the bolt, in its carrier would just close on the go gauge.

Two problems - while he didn't let the carrier slam home on the gauge, he did let the actions spring gently close on the gauge - way too much force to get an accurate measurement. Second problem is he just blew the chamber out with some shop air between gauging/cutting cycles.

Later when the chamber was closely inspected by somebody who knew what they were doing.... it was found to be about .005 over minimum, or actually a bit past the "no-go" point.

Which brings up - the lunacy of people have with headspace. I mean oh-my-God the headspace is .002 over maxium.... the barrel is ruined, and also... under no curcumstances should be be shot! Total and complete nonsense.

Anyway - be sure to have the chamber, gauge and bolt squeaky clean. Barrel extention squeaky clean. Be sure to turn the bolt onto the gauge as if you were trying to take a reading with a micrometer.... EASY ... its all by feel.

Suggested reading of course, is the chapter in Hatcher's Notebook, as well as the chapter on the Garand rifle's headspace issues in his book on the Garand. It all applies to the AR15's as well.
Link Posted: 3/4/2006 1:52:02 PM EDT
Which brings up - the lunacy of people have with headspace. I mean oh-my-God the headspace is .002 over maxium.... the barrel is ruined, and also... under no curcumstances should be be shot! Total and complete nonsense.



I quote you, sir, as an example of '...the lunacy people have with headspace'. If a chamber is beyond specification it is NOT safe to shoot. Charles the Gunsmith.
Link Posted: 3/4/2006 5:58:18 PM EDT

Originally Posted By 1911builder:
If a chamber is beyond specification it is NOT safe to shoot. Charles the Gunsmith.



So which specification is definitive? There is a .0036" difference from civi field to the Colt field gauge, that's over twice the difference of the civilian Go to NoGo gauges.

Civi NoGO (1.4670")
Civi Field (1.4700")
Military NoGo (1.4706" -0.0002")
Military Field (1.4730" -0.0002")
Colt Field II (1.4736")

Source
Link Posted: 3/4/2006 11:26:06 PM EDT

Originally Posted By 1911builder:
Which brings up - the lunacy of people have with headspace. I mean oh-my-God the headspace is .002 over maxium.... the barrel is ruined, and also... under no curcumstances should be be shot! Total and complete nonsense.

he



Man oh man... I beg to differ. Tell me what exactly happens if you've got .002 excessive headspace? Is it worse than having a cartridge who's shoulder is .002 further back than you might expect? Do we go around gauging cartridges? If we reload, we adjust the die to fit our chamber! But who has a ring gauge to measure a catridge (I do in fact! but only for .30-06, not .225/5.56).

Let me tell you that it is not uncommon to see ammo that is .005 or more shorter from shoulder to breechface than SAMMI minimim. Not uncommon at all. Especially S&B

This brings us to the rather push pull relationship of chamber makers vs ammo makers. Chamber makers (gun manufacturers) tend to go max chamber spec and I dare say "go over spec" at times. Reason? God forbid some ammo doesn't fit in their chamber. Match chambers excluded, other speciality chambers as well. Ammo makers... run the other end. They go minimim spec for the same reason in reverse. And I know factually that they run underspec in .30-06 and can only guess this is fairly common practice in other chamberings.

So again? What if you've got .002 extra headspace? Not safe to shoot.... not so. Not what we're hoping for in chamber size, but not the end of the world.
Link Posted: 3/4/2006 11:35:00 PM EDT
And.... that doesn't even begin to delve into what would be known as bolt overshoot, or the slack in the bolt travel needed to get it closed..... which has the effect of moving the shoulder back on any ammo lengthy enough to fully fill the chamber during cycling.

Whats the spec on overshoot on an AR15? I've never seen one published. I know on a Garand its incredibly small, the smallest of any rifle out there I've been told. Just a couple of thou. or so.

I know the springfield M1a's run hot and cold with overshoot, the better ones hold it pretty close.

I'd be interested to see what it is on an AR15
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