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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Custom action pressure ceiling.
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<blockquote data-quote="Pdvdh" data-source="post: 375195" data-attributes="member: 4191"><p>If the brass is unsupported by steel, it wouldn't matter what quality action or chamber it was in. The brass case head expansion would be controlled solely by the brass case strength and the pressures reached within the case during firing. </p><p></p><p>A very tight rifle chamber, if that chamber extended all the way back to enclose the cartridge case head? Maybe that would help. But the case heads aren't encased by the steel barrel chamber, at least on my bolt action rifles. That being the situation, unsupported & behind the steel chamber they will expand, and on a reliable basis.</p><p></p><p>I tend to believe the difference in a more stout action compared to a less stout action is more in longitudinal direction on the casing, than in the radial direction. By this I mean that a stronger barreled action assembly will stretch less in the case head to case shoulder direction, which allows the brass case less opportunity to stretch in that direction also. If the bolt is set back somewhat under peak pressures, this also allows the case to expand longitudinally from the case head to the case shoulder. After the pressure subsides, the brass has stretched so much that the lugs on the bolt remain loaded due to the lengthening of the case, similar to trying to close the bolt on a casing that hasn't been resized sufficiently. This accounts for some of the difficult bolt lift in a weaker barreled action than with a stronger barreled action. </p><p></p><p>Now the casing will also expand radially to a greater extent under greater pressures, and can do so under enough pressure and/or repeated firings such that the brass doesn't relax after firing, resulting in difficult extraction. But to the extent that radial casing and case head expansion is controlled by the barrel chamber or action, it is controlled more by the barrel chamber than the action. Again - in my opinion. Barrels are threaded into the receiver, and that threaded joint itself allows momentary barrel chamber expansion before the action that the barrel is threaded into could assist in preventing further radial barrel chamber & radial case expansion. The best way to minimize high pressure caused case swelling (and chamber swelling) in the radial direction is a larger outside diameter barrel - particularly the threaded tennon portion of the barrel where the barrel is machined down to its smallest outer diameter. This is possible with larger diameter barrel threads - which requires a larger diameter action and action threads. Or expressed another way, an action with a larger diameter barrel thread size will assist in reducing radial case swelling (of the portion of the case contained within the steel chamber), not so much due to the radial strength of the action itself, but because the larger thread size will result in a larger outside diameter of the threaded tennon of the barrel surrounding the cartridge casing. The larger OD barrel (greater cross section of steel) will better resist (and reduce) the momentary elastic swelling of the barrel surrounding the cartridge case at the moment of peak chamber pressure.</p><p></p><p>That's my take on it. My opinion. It's subject to change given sufficient explanation and cause otherwise.</p></blockquote><p></p>
[QUOTE="Pdvdh, post: 375195, member: 4191"] If the brass is unsupported by steel, it wouldn't matter what quality action or chamber it was in. The brass case head expansion would be controlled solely by the brass case strength and the pressures reached within the case during firing. A very tight rifle chamber, if that chamber extended all the way back to enclose the cartridge case head? Maybe that would help. But the case heads aren't encased by the steel barrel chamber, at least on my bolt action rifles. That being the situation, unsupported & behind the steel chamber they will expand, and on a reliable basis. I tend to believe the difference in a more stout action compared to a less stout action is more in longitudinal direction on the casing, than in the radial direction. By this I mean that a stronger barreled action assembly will stretch less in the case head to case shoulder direction, which allows the brass case less opportunity to stretch in that direction also. If the bolt is set back somewhat under peak pressures, this also allows the case to expand longitudinally from the case head to the case shoulder. After the pressure subsides, the brass has stretched so much that the lugs on the bolt remain loaded due to the lengthening of the case, similar to trying to close the bolt on a casing that hasn't been resized sufficiently. This accounts for some of the difficult bolt lift in a weaker barreled action than with a stronger barreled action. Now the casing will also expand radially to a greater extent under greater pressures, and can do so under enough pressure and/or repeated firings such that the brass doesn't relax after firing, resulting in difficult extraction. But to the extent that radial casing and case head expansion is controlled by the barrel chamber or action, it is controlled more by the barrel chamber than the action. Again - in my opinion. Barrels are threaded into the receiver, and that threaded joint itself allows momentary barrel chamber expansion before the action that the barrel is threaded into could assist in preventing further radial barrel chamber & radial case expansion. The best way to minimize high pressure caused case swelling (and chamber swelling) in the radial direction is a larger outside diameter barrel - particularly the threaded tennon portion of the barrel where the barrel is machined down to its smallest outer diameter. This is possible with larger diameter barrel threads - which requires a larger diameter action and action threads. Or expressed another way, an action with a larger diameter barrel thread size will assist in reducing radial case swelling (of the portion of the case contained within the steel chamber), not so much due to the radial strength of the action itself, but because the larger thread size will result in a larger outside diameter of the threaded tennon of the barrel surrounding the cartridge casing. The larger OD barrel (greater cross section of steel) will better resist (and reduce) the momentary elastic swelling of the barrel surrounding the cartridge case at the moment of peak chamber pressure. That's my take on it. My opinion. It's subject to change given sufficient explanation and cause otherwise. [/QUOTE]
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