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Rifles, Reloading, Optics, Equipment
Reloading
Mechanics of a crush fit
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<blockquote data-quote="Mikecr" data-source="post: 944072" data-attributes="member: 1521"><p>HS setback on primer firing only occurs with disposable case designs holding very low shoulder angles & high body taper (243, 270, 308, 30-06, etc). In these cases it takes little to nothing to wedge and vary the angles. An exception to this, there always is, something like a 223 where relative thickness to case area is high. So even though a 223 holds a low shoulder angle, it doesn't setback on primer firing. And with a rational load, you can crush fit it for all eternity. Not so with the same thickness in 308 capacity.</p><p></p><p>Newer cartridges with 30deg shoulders are more reloader friendly. </p><p>These also do not set back in HS on primer firing. The price(there always is)? They cannot be counted on to self-center on firing in chambers with excess clearances, and when loaded TIR is high.</p><p>So they are way easier to make and maintain with precision, but also need to be (less forgiving).</p><p></p><p>It's not easy to see brass gripping walls whether front-to-back, or back-to-front, until measuring variances from fully fire-formed. I imagine this dynamic again changes with case design & headspacing system.</p><p>I know with fully FF'd cases of modern design, having very high shoulder angles and very low body taper, normal load pressures, enough barrel steel around chamber, and held within normal springback for clearances, no dimensions yield and sizing is no longer required at all.</p><p>This is where I like to be.</p></blockquote><p></p>
[QUOTE="Mikecr, post: 944072, member: 1521"] HS setback on primer firing only occurs with disposable case designs holding very low shoulder angles & high body taper (243, 270, 308, 30-06, etc). In these cases it takes little to nothing to wedge and vary the angles. An exception to this, there always is, something like a 223 where relative thickness to case area is high. So even though a 223 holds a low shoulder angle, it doesn't setback on primer firing. And with a rational load, you can crush fit it for all eternity. Not so with the same thickness in 308 capacity. Newer cartridges with 30deg shoulders are more reloader friendly. These also do not set back in HS on primer firing. The price(there always is)? They cannot be counted on to self-center on firing in chambers with excess clearances, and when loaded TIR is high. So they are way easier to make and maintain with precision, but also need to be (less forgiving). It's not easy to see brass gripping walls whether front-to-back, or back-to-front, until measuring variances from fully fire-formed. I imagine this dynamic again changes with case design & headspacing system. I know with fully FF'd cases of modern design, having very high shoulder angles and very low body taper, normal load pressures, enough barrel steel around chamber, and held within normal springback for clearances, no dimensions yield and sizing is no longer required at all. This is where I like to be. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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Mechanics of a crush fit
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