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Old January 26, 2020, 05:57 PM   #267
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Join Date: June 17, 2010
Location: Virginia
Posts: 5,631
It's not a mystery--SAAMI specs as submitted by winchester specify a max headspace of 1.720.
If the top of your case head will not be supported by the chamber--you are tossing the dice.
Apples vs Oranges.

A. AR straightwall headspace is simply bolt-face-to-case-mouth stop. SAAMI: 1.710-1.720"
B. The problem is bolt face distance to chamber transition/start SAAMI: 0.200" ... two different measurements.

As long as the bolt face forces the cartridge in far enough to have the web floor safely/fully clear the chamfer cutout, everything's fine. (case length/headspace is irrelevant)
When the web floor is left hanging out there, however (B. above > 0.200"),* then you gotta problem no matter what.

Two ways that can happen:
- Bolt face is too far back from chamfer/chamber transition
- Chamfer is cut too deeply into the chamber

I'm beginning to think that the chamfer cut is the problem.

* Or.... the case head thickness (base-to-web-floor) is << 0.200"

Last edited by mehavey; January 26, 2020 at 06:47 PM.
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