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The Basics, Starting Out
Question: Reamer Dimensions vs Chamber Dimensions vs Case Dimensions
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<blockquote data-quote="Batsin" data-source="post: 3052890" data-attributes="member: 126867"><p>This is an area that causes problems with the current SAAMI specs, though. The assumption is that every rifle can crush fit the case into battery whereas many, especially autoloaders, cannot consistently do so and operate as designed. That is why I have been surprised that this crush fit dimension has been left in for cartridges that have been designed specifically around the AR15 platform, for instance. A very small change in the specifications would avoid this problem.</p><p>Cartridges like the 6.5 Grendel and the newer 22 and 6mm ARC were designed around the magazine length and bolt-strength limitations of the AR15 platform. The SAAMI max chamber pressure of 52,000psi (transducer) reflects that. It seems odd, then, that other tolerances were not also adapted. An in-spec case can still require a crush fit into an in-spec chamber. </p><p></p><p>FWIW, I re-read my own posts and realized that a couple of things were not clear. The headspace dimensions in post #1 are for the 308 family.</p><p>In post #3, I intended to convey that the new 300 Norma Mag and 300 PRC spec bullets SMALLER the traditional dimension. The max bullet diameter for the 300 NM, for example, is called out in the SAAMI drawing as 0.3083" (same as the Weatherby Magnum) vs .3090" for most other .30 cal cartridges.</p></blockquote><p></p>
[QUOTE="Batsin, post: 3052890, member: 126867"] This is an area that causes problems with the current SAAMI specs, though. The assumption is that every rifle can crush fit the case into battery whereas many, especially autoloaders, cannot consistently do so and operate as designed. That is why I have been surprised that this crush fit dimension has been left in for cartridges that have been designed specifically around the AR15 platform, for instance. A very small change in the specifications would avoid this problem. Cartridges like the 6.5 Grendel and the newer 22 and 6mm ARC were designed around the magazine length and bolt-strength limitations of the AR15 platform. The SAAMI max chamber pressure of 52,000psi (transducer) reflects that. It seems odd, then, that other tolerances were not also adapted. An in-spec case can still require a crush fit into an in-spec chamber. FWIW, I re-read my own posts and realized that a couple of things were not clear. The headspace dimensions in post #1 are for the 308 family. In post #3, I intended to convey that the new 300 Norma Mag and 300 PRC spec bullets SMALLER the traditional dimension. The max bullet diameter for the 300 NM, for example, is called out in the SAAMI drawing as 0.3083" (same as the Weatherby Magnum) vs .3090" for most other .30 cal cartridges. [/QUOTE]
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The Basics, Starting Out
Question: Reamer Dimensions vs Chamber Dimensions vs Case Dimensions
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