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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: 488684" data-attributes="member: 5302"><p>Here's what happens in my own (and virtually all others I know of) SAAMI minimum spec'd chambers and fired .308 Win. cases that are full length resized reducing body diameters about 2 thousandths, setting the case shoulder back 2 thousandths and the FL die's neck sizing the whole case neck down such that the case mouth's about 1/1000th inch smaller than bullet diameter.</p><p></p><p>When the round's chambered and bolt closed, the inline ejector's spring pushes the case forward until its shoulder stops in the chamber shoulder. When the firing pin strikes the primer, that further drives the case shoulder hard into the chamber shoulder. The front of the case gets well centered in the chamber at the shoulder because the shoulder shape of both are the same; centering is very precice. And the case neck's also well centered in the chamber neck as it's centered on the case shoulder. Doesn't matter how much clearance there is around the case neck to the chamber neck; centered is centered. Note that the case shoulder typically gets set back a thousandth or more when the firing pin strikes with its 25 to 30 pound force. </p><p></p><p>At the back end where the extractor's pushing the case head up (for bolt face estractors that slide sideways such as the Winchester push-feed ones, sideways for Mauser style claw extractors that push the case sideways) until the case stops against the chamber wall. In some instances, the case rim will stop against the bolt face shroud if its tolerances and that of the chamber and case rim allow. But the case head always goes to the same point. Doesn't matter if the back end of the case is a thousandths or two off chamber center; it's repeatable and that is what's important..</p><p></p><p>With a round with zero bullet runout and its shoulder firmly well centered in the chamber shoulder, for each 1/1000th inch off center the case head is, the bullet tip will be about half that amount. More importantly, every round's seated in the chamber at the same angle and direction. The system's very repeatable.</p><p></p><p>As all cases and chambers are not perfectly round, it's a good idea to ensure no part of the case body interferes with the chamber walls. Full length sizing the fired case body does this. And the fired case body diameters need be sized down more than 2/1000ths. </p><p></p><p>Put a primed case in your rifle, then put a long rod down the muzzle so it rests on the case bottom around the flash hole. With a dial indicator set to measure how much the rod moves in and out of the barrel, you can usually push the rod down compressing the ejector spring and the case head will stop against the bolt face. Release the rod and it'll stop going out when the case shoulder stops against the chamber shoulder. The difference between these two measurements is the clearance your case headspace has to chamber headspace.</p><p></p><p>You can also use a case headspace gage (RCBS Prec. Mic?) to measure how much a primed rimless bottleneck case shoulder gets set back from firing pin impact. Ensure your firing pin spring is at factory specs for rating and the firing pin protrudes 50 to 60 thousandths from the bolt face in its fired position. Use a magic marker to blacken the shoulder of a primed case, chamber it, then remove it and you'll see the slightest marks where the ink shows contact with the chamber shoulder. Rechamber that primed case then fire it; the black ink now shows well defined marks showing it got driven hard into the chamber shoulder.</p><p></p><p>I learned this from Sierra Bullets first ballistic technician who reloaded cases testing most of their bullets from the 1950's though the middle 1980's. And my own various tests prove it so.</p></blockquote><p></p>
[QUOTE="Bart B, post: 488684, member: 5302"] Here's what happens in my own (and virtually all others I know of) SAAMI minimum spec'd chambers and fired .308 Win. cases that are full length resized reducing body diameters about 2 thousandths, setting the case shoulder back 2 thousandths and the FL die's neck sizing the whole case neck down such that the case mouth's about 1/1000th inch smaller than bullet diameter. When the round's chambered and bolt closed, the inline ejector's spring pushes the case forward until its shoulder stops in the chamber shoulder. When the firing pin strikes the primer, that further drives the case shoulder hard into the chamber shoulder. The front of the case gets well centered in the chamber at the shoulder because the shoulder shape of both are the same; centering is very precice. And the case neck's also well centered in the chamber neck as it's centered on the case shoulder. Doesn't matter how much clearance there is around the case neck to the chamber neck; centered is centered. Note that the case shoulder typically gets set back a thousandth or more when the firing pin strikes with its 25 to 30 pound force. At the back end where the extractor's pushing the case head up (for bolt face estractors that slide sideways such as the Winchester push-feed ones, sideways for Mauser style claw extractors that push the case sideways) until the case stops against the chamber wall. In some instances, the case rim will stop against the bolt face shroud if its tolerances and that of the chamber and case rim allow. But the case head always goes to the same point. Doesn't matter if the back end of the case is a thousandths or two off chamber center; it's repeatable and that is what's important.. With a round with zero bullet runout and its shoulder firmly well centered in the chamber shoulder, for each 1/1000th inch off center the case head is, the bullet tip will be about half that amount. More importantly, every round's seated in the chamber at the same angle and direction. The system's very repeatable. As all cases and chambers are not perfectly round, it's a good idea to ensure no part of the case body interferes with the chamber walls. Full length sizing the fired case body does this. And the fired case body diameters need be sized down more than 2/1000ths. Put a primed case in your rifle, then put a long rod down the muzzle so it rests on the case bottom around the flash hole. With a dial indicator set to measure how much the rod moves in and out of the barrel, you can usually push the rod down compressing the ejector spring and the case head will stop against the bolt face. Release the rod and it'll stop going out when the case shoulder stops against the chamber shoulder. The difference between these two measurements is the clearance your case headspace has to chamber headspace. You can also use a case headspace gage (RCBS Prec. Mic?) to measure how much a primed rimless bottleneck case shoulder gets set back from firing pin impact. Ensure your firing pin spring is at factory specs for rating and the firing pin protrudes 50 to 60 thousandths from the bolt face in its fired position. Use a magic marker to blacken the shoulder of a primed case, chamber it, then remove it and you'll see the slightest marks where the ink shows contact with the chamber shoulder. Rechamber that primed case then fire it; the black ink now shows well defined marks showing it got driven hard into the chamber shoulder. I learned this from Sierra Bullets first ballistic technician who reloaded cases testing most of their bullets from the 1950's though the middle 1980's. And my own various tests prove it so. [/QUOTE]
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How do you straighten runout?
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