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Posted: 6/1/2004 2:37:58 PM EDT
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I keep seeing reference to "primary extraction" (as part of the firing cycle). Can somebody explain what this term means? jafager |
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Primary extraction refers to the first movement of the case in the chamber after firing. This is the movement that "breaks", or unsticks the case before it's fully extracted. On most rifles, the bolt rotates, and in the very first part of the rotation, it moves backward slightly. This slight backward movement is the "primary extraction" that breaks the case's adhesion to the chamber walls. Once the case is loosened in the chamber, the bolt can than easily extract it. |
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Some types of gun mechanisms - the blowback family - lack primary extraction because they are dependent on the chamber pressure pushing the cartridge case out of the chamber. So guns using high-pressure loadings (as found in some MGs and automatic cannon) are prone to cases sticking in the chambers. They used to get around this by oiling or waxing cases, but now they used fluted chambers - there are narrow grooves in the chamber walls leading back from the case mouth to allow some gas to flow around the outside of the case. Tony Williams: Military gun and ammunition website and discussion forum |
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