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Rifles, Reloading, Optics, Equipment
Reloading
How do you straighten runout?
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<blockquote data-quote="Bart B" data-source="post: 492909" data-attributes="member: 5302"><p>In all the rifle's I've used, here's how the case fits the chambers:</p><p></p><p>1. Extractors all push the case sideways against the lip of the bolt face. The bolt face diameter's larger than the back end of the chamber. So when a round's chambered, the extractor pushes the case against the chamber wall. </p><p></p><p>2. The clearance between bolt face and extractory lip is always more than case rim thickness. There's no way any extractor I know of to hold the case head against the bolt face. There has to be ample clearance between bolt face and extractor lip to allow the thickenst rimmed case to easily slide in when the round's loaded. (Go measure your own rifle bolts and rim thickness to see what the difference is.) After the round's chambered, there would have to be some force pulling the extractor back such that it pulls the case back against the bolt face. I don't know of any extractors that pull the case hard against the bolt face hard enough to keep it there when 25 to 35 pounds of force smack the primer.</p><p></p><p>3. All my rimless bottleneck cases from 22 through 30 caliber have always had their shoulders set back a thousandth or more when the firing pin strikes the primer. How much depends on firing pin spring strength, firing pin protrusion from bolt face, firing pin tip shape, primer cup hardness, shoulder area and angle, and the friction coefficient between case and chamber shoulder. Loads with 10% or more reduced powder charges typically end up leaving the primer pushed out of the case and case headspace is less after firing than before; proof the case fired with the case head forward of the bolt face. I've measured too many such primed cases without bullet and powder to see how much their shoulders get set back by firing pin impact. I was amazed when I first measured them. So there's no way my extractors were holding the case head against the bolt face.</p><p></p><p>4. When a rimless bottleneck case is struck by a firing pin, it gets driven forward into the chamber an amount equal to chamber headspace minus case headspace. The force sets the shoulder back lengthing the case neck. And because case and chamber shoulders have the same angle, this perfectly centers the front of the case in the chamber. When the round fires, the case head is a few thousandths further away from the bolt face and the case expands to fit the chamber starting at the thinnest part of the case first at its front end. The primer is also pushed back out of its pocket. As pressure builds and the bullet starts down the bore, the case expands more pushing the back of the case against the bolt face seating the primer as well as pushing the case against the chamber wall. As the case expands fully against the chamber wall, it draws brass back out of the neck and shoulder area shortening the case. All such cases are typically shorter after firing's complete. They lengthen when resized; a little with neck only, more with full length sizing.</p><p></p><p>5. Headspace is the distance between the bolt face and the chamber point that limits case movement forward in the chamber; according to SAAMI standards/specifications/glossary. Head clearance is the difference between chamber headspace and the same measurement on the case; the space between the bolt face and case head when the round fires. Let's not get these two terms confused.</p></blockquote><p></p>
[QUOTE="Bart B, post: 492909, member: 5302"] In all the rifle's I've used, here's how the case fits the chambers: 1. Extractors all push the case sideways against the lip of the bolt face. The bolt face diameter's larger than the back end of the chamber. So when a round's chambered, the extractor pushes the case against the chamber wall. 2. The clearance between bolt face and extractory lip is always more than case rim thickness. There's no way any extractor I know of to hold the case head against the bolt face. There has to be ample clearance between bolt face and extractor lip to allow the thickenst rimmed case to easily slide in when the round's loaded. (Go measure your own rifle bolts and rim thickness to see what the difference is.) After the round's chambered, there would have to be some force pulling the extractor back such that it pulls the case back against the bolt face. I don't know of any extractors that pull the case hard against the bolt face hard enough to keep it there when 25 to 35 pounds of force smack the primer. 3. All my rimless bottleneck cases from 22 through 30 caliber have always had their shoulders set back a thousandth or more when the firing pin strikes the primer. How much depends on firing pin spring strength, firing pin protrusion from bolt face, firing pin tip shape, primer cup hardness, shoulder area and angle, and the friction coefficient between case and chamber shoulder. Loads with 10% or more reduced powder charges typically end up leaving the primer pushed out of the case and case headspace is less after firing than before; proof the case fired with the case head forward of the bolt face. I've measured too many such primed cases without bullet and powder to see how much their shoulders get set back by firing pin impact. I was amazed when I first measured them. So there's no way my extractors were holding the case head against the bolt face. 4. When a rimless bottleneck case is struck by a firing pin, it gets driven forward into the chamber an amount equal to chamber headspace minus case headspace. The force sets the shoulder back lengthing the case neck. And because case and chamber shoulders have the same angle, this perfectly centers the front of the case in the chamber. When the round fires, the case head is a few thousandths further away from the bolt face and the case expands to fit the chamber starting at the thinnest part of the case first at its front end. The primer is also pushed back out of its pocket. As pressure builds and the bullet starts down the bore, the case expands more pushing the back of the case against the bolt face seating the primer as well as pushing the case against the chamber wall. As the case expands fully against the chamber wall, it draws brass back out of the neck and shoulder area shortening the case. All such cases are typically shorter after firing's complete. They lengthen when resized; a little with neck only, more with full length sizing. 5. Headspace is the distance between the bolt face and the chamber point that limits case movement forward in the chamber; according to SAAMI standards/specifications/glossary. Head clearance is the difference between chamber headspace and the same measurement on the case; the space between the bolt face and case head when the round fires. Let's not get these two terms confused. [/QUOTE]
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