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Rifles, Reloading, Optics, Equipment
Reloading
'Flattened' primer pictures?
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<blockquote data-quote="CatShooter" data-source="post: 126241" data-attributes="member: 7"><p><strong>Re: \'Flattened\' primer pictures?</strong></p><p></p><p>Flattened primers are not always a sign of pressure - more often, they are a sign of head space.</p><p></p><p>To read pressure, you need to take into account many signs all at once.</p><p></p><p>Cratering of the primer: Assuming that normal factory loads DON'T crater, then cratering is a sign that you are pushing it. These days, with the loose tolerances of manufacturers, some bolt pin holes are way oversized and will crater with light or factory loads.</p><p></p><p>Flat primers: Assuming a normal rifle with a proper sized pin hole... cases will crater before the outside edges start to smear out to the case and get a sharp edge. So with cratering and flat primers it is clearly a case of excess pressure.</p><p></p><p>BUT... in most situations, there is some space between the bolt face, and the brass. Even a rifle that is "in spec" can have as much as 0.025" of headspace... in fact it is extreamly rare that a rifle has "0.000" headspace.</p><p></p><p>With this space, when the cartridge is fired, the primer pushes the case forwards 'til it hits the shoulder, during which time the powder lights. At this stage, the primer is sticking out of the case by the amount of headspace - (ei 0.025"). The pressure in the case then forces the case back against the bolt face.</p><p></p><p>NOW... if the primer walls are firm against the pocket walls, then the protruding primer gets squshed and flattens out - but there is no excess pressure.</p><p></p><p>So, in order to use flatened primers as a pressure sign, they must also be read with other signs.... mostly cratering.</p><p></p><p>Reading primers is an art, not a science.</p><p></p><p></p><p>.</p></blockquote><p></p>
[QUOTE="CatShooter, post: 126241, member: 7"] [b]Re: \'Flattened\' primer pictures?[/b] Flattened primers are not always a sign of pressure - more often, they are a sign of head space. To read pressure, you need to take into account many signs all at once. Cratering of the primer: Assuming that normal factory loads DON'T crater, then cratering is a sign that you are pushing it. These days, with the loose tolerances of manufacturers, some bolt pin holes are way oversized and will crater with light or factory loads. Flat primers: Assuming a normal rifle with a proper sized pin hole... cases will crater before the outside edges start to smear out to the case and get a sharp edge. So with cratering and flat primers it is clearly a case of excess pressure. BUT... in most situations, there is some space between the bolt face, and the brass. Even a rifle that is "in spec" can have as much as 0.025" of headspace... in fact it is extreamly rare that a rifle has "0.000" headspace. With this space, when the cartridge is fired, the primer pushes the case forwards 'til it hits the shoulder, during which time the powder lights. At this stage, the primer is sticking out of the case by the amount of headspace - (ei 0.025"). The pressure in the case then forces the case back against the bolt face. NOW... if the primer walls are firm against the pocket walls, then the protruding primer gets squshed and flattens out - but there is no excess pressure. So, in order to use flatened primers as a pressure sign, they must also be read with other signs.... mostly cratering. Reading primers is an art, not a science. . [/QUOTE]
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'Flattened' primer pictures?
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