Headspace - THR

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Old January 11, 2006, 06:25 PM   #1
Join Date: May 22, 2003
Location: Lexington,North Carolina...or thereabouts
Posts: 18,465

In light of realizing that so many good folks are misinformed on the subject of correct headspacing in the 1911 pistol, I took the liberty of doin' this thread in the interest of our continuing education, so that all may be armed with the knowledge to make a call of: "SHEEPDIP!" whenever some gunshop
commando drops a round into a barrel chamber...shows that the rear of the rim is flush with the face of the hood...and pronounces it good to go. While that condition may well exist in a pistol with perfectly acceptable headspace,
that, in and of itself, is NOT an indication.

Headspace falls into two categories.

Static headspace is the measurement between the breechface and the cartridge stop shoulder with the pistol in battery. Static headspace only changes with wear and/or locking lug deformation or setback...or wear on the breechface.

Live...or working headspace is the difference between that measurement and the length of the cartridge case that is fired in the gun...and varies with every shot unless all brass is trimmed to exactly the same length.

Excessive headspace is defined as static headspace that falls outside of acceptable limits as set by the SAAMI for the caliber. Static headspace is correctly determined with a gauge...typically GO and NO-GO. Precisely measuring headpace requires a determination of the exact dimension, usually done by using a GO gauge and an appropriate feeler gauge in conjunction.
GO...plus feeler gauge thickness equals total static headspace.

Headspace limit for the 1911 pistol is .898 inch minimum and .920 maximum. GO and NO-GO sets are made to these specifications.

Headspace can be excessive and still be safe. It can be excessive and be dangerous. It depends on which direction that the excess goes.

If the stop shoulder is reamed too deep in the chamber, it can be outside ot the maximum limit, yet still be safe. If the locking lugs are incorrectly located,
incorrectly cut, or deformed...the excess can be dangerous , because it allows partial opening of the breech on firing. The case backs out of the chamber until the slide reaches the limit of its rearward travel as determined by the horizontal lug to lug fit...and the case head loses chamber support.

You can ream the chamber too far...file the hood to perfectly flush with a chambered round or GO gauge...and it will look like good headspace...but it's not.

You can ream the chamber perfectly at minimum dimension...with a cartridge
or GO gauge dead flush with the hood face...and if the lug fit allows the breech to partially open beyond NO-GO limits on firing, you have a dangerously excessive headspace condition.

To better understand this, we need to understand that when the pistol fires, the slide and barrel are tied together by the horizontal lug engagement. The barrel is slammed forward by the bullet while the thrust of the expanding gasses are driving the slide rearward in a 20,000 psi tug of war...and are doing their level best to separate the slide and barrel. If the lugs allow the slide to move rearward beyond safe limits...NO-GO...the case follows the breechface...loses chamber support at 6 O'Clock...and bulges or blows.

Hope this clears things up a little.

Carry on!

Speak kindly to me, beloved master. Revel in my unconditional love, and give me every minute that you can spare, for my time with you is short.

-your faithful dog-

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