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Old October 7, 2013, 08:18 PM   #41
Bart B.
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Join Date: February 15, 2009
Posts: 8,927
One can easily deduce from the following SAAMI specs:

http://www.saami.org/PubResources/CC...Winchester.pdf

...that the average loaded round case headspace is 2.0491" and the average chamber headspace is 2.0537". So the average head clearance (bolt face to case head when the headspacing part of the case is against the headspacing part of the chamber) with such a round in such a chamber will be .0046" That'll allow the case shoulder to slam hard into the chamber shoulder when the firing pin hits it long before the firing pin reaches its maximum protrusion from the bolt face at somewhere between .050" and .065" when it dents the primer cup at least .040". To say nothing about in-line ejectors pushing the chambered round full forward in the chamber before the firing pin falls and there's the same amount of head clearance. Similar dimensional issues exist with other cartridges and can be easily seen by checking out other cartridge and chamber mechanical drawings from SAAMI specs. Even with a minimum dimensioned case and maximum dimensioned chamber, the case will still stop its forward movement as it contacts the chamber's headspace point and allow the firing pin to dent the primer well beyond the minimum required to fire it. Make measurements on your stuff like I've done and you'll easily see what your stuff does.

Note also the .270's bore diameter SAAMI specs are .270" +.002" and that's a greater spread than the .0015" stated by Savage. The groove diameter also has a .002" spread. No wonder so many folks get muzzle velocities and pressures much lower than what SAAMI spec test barrels produce for a given load.

Last edited by Bart B.; October 8, 2013 at 06:29 AM.
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