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Rifles, Reloading, Optics, Equipment
Reloading
Headspace Datum Line?
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<blockquote data-quote="Trickymissfit" data-source="post: 702171" data-attributes="member: 25383"><p>I always CAD out a once fired case (actually five cases), and setup my own set of numbers. Try to split the difference between the neck O.D. and the shoulder diameter; give or take .010". This becomes my own gauge dine and I then calculate the distance from the face of the case to the gauge line. Thus creating the gauge line deminsion. I may adjust the length a couple thousandths as things begine to settle in, but rarely more than four thousandths, and usually less than two. I donot trust generic headspace gauges for this as chambers will vary slightly. You culd probably use something like a 12mm or even a 7/16" inner race from a needle bearing as long as it's longer than the neck. (you know right upfront that the faces on an inner race are parallel). Or simply make your own in a lathe.</p><p> </p><p>You are correct in bumping the shoulder back .002" to .003", but that number becomes generic if you base everything off an existing drawing. I prefer to do this by chambering a case in the rifle looking for a slight bit of resistence while I close the bolt. Then I bump everything back from there. I also will vary the amount of bump per individual chambering. (I only bump .222's and .223's back about .001" max). I keep a log book on what I do here as I'm getting old now!</p><p> </p><p>I might also add here (although slightly off topic) that one of the first things I do is to find out just how long the actual neck is in the chamber, and setup a max overall length from that distance; minus .015" (I hate trimming cases almost as much as I hate reaming primer pockets)</p><p>gary</p></blockquote><p></p>
[QUOTE="Trickymissfit, post: 702171, member: 25383"] I always CAD out a once fired case (actually five cases), and setup my own set of numbers. Try to split the difference between the neck O.D. and the shoulder diameter; give or take .010". This becomes my own gauge dine and I then calculate the distance from the face of the case to the gauge line. Thus creating the gauge line deminsion. I may adjust the length a couple thousandths as things begine to settle in, but rarely more than four thousandths, and usually less than two. I donot trust generic headspace gauges for this as chambers will vary slightly. You culd probably use something like a 12mm or even a 7/16" inner race from a needle bearing as long as it's longer than the neck. (you know right upfront that the faces on an inner race are parallel). Or simply make your own in a lathe. You are correct in bumping the shoulder back .002" to .003", but that number becomes generic if you base everything off an existing drawing. I prefer to do this by chambering a case in the rifle looking for a slight bit of resistence while I close the bolt. Then I bump everything back from there. I also will vary the amount of bump per individual chambering. (I only bump .222's and .223's back about .001" max). I keep a log book on what I do here as I'm getting old now! I might also add here (although slightly off topic) that one of the first things I do is to find out just how long the actual neck is in the chamber, and setup a max overall length from that distance; minus .015" (I hate trimming cases almost as much as I hate reaming primer pockets) gary [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
Headspace Datum Line?
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