Over the years, one of the most common misconceptions I've run into is headspace in the 1911 pistol where somebody will drop a live round into the barrel, and call headspace good or bad by whether the rear face of the rim sits flush with the rear face of the barrel hood.
The only problem is that the barrel hood has nothing at all to do with headspace. The barrel hood serves only two purposes. It's a dust cover, and it works with the slide to push the barrel forward and up into engagement with the slide.
Headspace is defined as the gap between the breechface and the rear face of the case rim when the cartridge is as far forward in the chamber as it can go with the slide in full battery.
The static headspace dimension...the dimension that doesn't change except through wear or lug deformation...is the linear distance between the breechface and the cartridge stop shoulder. The dynamic or "working" headspace dimension varies from shot to shot with the length of a given cartridge case.
As an example...with a minimum static dimension of .898 inch, if a round with a case length of .888 is in the chamber, you have .010 inch of headspace. If the next round has a case length of .885, yiou have .013 inch of headspace and so on.
Due to relatively low pressures, the 1911 has a pretty generous headspace tolerance. Minimum is .898 and maximum is .920 inch static and is tested with GO and NO GO gauges that are .898 and .920 inch long respectively. With the extractor removed, all pistols must go to full battery on the GO gauge, and none may go to full battery on the NO GO. This is tested without forcing the slide beyond what the recoil spring will provide with the slide guided forward gently.
Moreover, the gauges will only tell us if the headspace is outside of allowable tolerances. It doesn't tell us why. That has to be determined by closer examination.
Example: Failing on the GO gauge is most often a simple matter of a short chamber which is easy to correct with a finishing reamer. Failing on the NO GO may be a simple matter of an overcut chamber...too deep...and likely won't present a dangerous headspace condition, though if excessive enough could result in misfires. Or, it could be due to lug deformation or mislocation, and very well could be a dangerous condition if the gun is fired.
It's also possible...rare but theoretically possible...for the gun to pass both gauge tests and still present a dangerous headspace condition. i.e a good chamber with slide lugs deformed to the rear far enough to allow the case to back up on firing and lose case support at the bottom in the barrel ramp area. This is why, when rebarreling a high mileage pistol, measuring the slide lug locations relative to the breechface is critical. Deformed lugs are usually apparent with flanging and obvious damage...but not always.
Any bulging of fired cases on one side just forward of the webbing is a red flag and cause to stop firing the gun and check for excessive headspace. Note that this can also happen with a barrel that's been excessively "throated" in a misguided attempt to correct a problem with go to or return to battery. ..which most often comes after someone wrecked the feed ramp angle with a Dremel...recognized the resulting problem...and tried to compensate by then progressively removing metal from the bottom of the chamber until the pistol returns to battery reliably.
The only problem is that the barrel hood has nothing at all to do with headspace. The barrel hood serves only two purposes. It's a dust cover, and it works with the slide to push the barrel forward and up into engagement with the slide.
Headspace is defined as the gap between the breechface and the rear face of the case rim when the cartridge is as far forward in the chamber as it can go with the slide in full battery.
The static headspace dimension...the dimension that doesn't change except through wear or lug deformation...is the linear distance between the breechface and the cartridge stop shoulder. The dynamic or "working" headspace dimension varies from shot to shot with the length of a given cartridge case.
As an example...with a minimum static dimension of .898 inch, if a round with a case length of .888 is in the chamber, you have .010 inch of headspace. If the next round has a case length of .885, yiou have .013 inch of headspace and so on.
Due to relatively low pressures, the 1911 has a pretty generous headspace tolerance. Minimum is .898 and maximum is .920 inch static and is tested with GO and NO GO gauges that are .898 and .920 inch long respectively. With the extractor removed, all pistols must go to full battery on the GO gauge, and none may go to full battery on the NO GO. This is tested without forcing the slide beyond what the recoil spring will provide with the slide guided forward gently.
Moreover, the gauges will only tell us if the headspace is outside of allowable tolerances. It doesn't tell us why. That has to be determined by closer examination.
Example: Failing on the GO gauge is most often a simple matter of a short chamber which is easy to correct with a finishing reamer. Failing on the NO GO may be a simple matter of an overcut chamber...too deep...and likely won't present a dangerous headspace condition, though if excessive enough could result in misfires. Or, it could be due to lug deformation or mislocation, and very well could be a dangerous condition if the gun is fired.
It's also possible...rare but theoretically possible...for the gun to pass both gauge tests and still present a dangerous headspace condition. i.e a good chamber with slide lugs deformed to the rear far enough to allow the case to back up on firing and lose case support at the bottom in the barrel ramp area. This is why, when rebarreling a high mileage pistol, measuring the slide lug locations relative to the breechface is critical. Deformed lugs are usually apparent with flanging and obvious damage...but not always.
Any bulging of fired cases on one side just forward of the webbing is a red flag and cause to stop firing the gun and check for excessive headspace. Note that this can also happen with a barrel that's been excessively "throated" in a misguided attempt to correct a problem with go to or return to battery. ..which most often comes after someone wrecked the feed ramp angle with a Dremel...recognized the resulting problem...and tried to compensate by then progressively removing metal from the bottom of the chamber until the pistol returns to battery reliably.
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