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Rifles, Reloading, Optics, Equipment
Reloading
Case weight variability question
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<blockquote data-quote="QuietTexan" data-source="post: 2192560" data-attributes="member: 116181"><p>Probably more to do with a higher portion of energy in the shot going to forming the full case body against the chamber. Especially if you aren't FL sizing going forward, the initial shot affects more brass than subsequent shots, especially if you don't FL size to a minimum spec going forward because most of the case is not sized down before subsequent shots. </p><p></p><p>My thought process (with kind-of guessed at numbers): If the difference in the case and chamber is .0015", the case body moves .0015" radially on the initial shot. Let's say it springs back a full ".0010, it's .0005 larger than before, and then it then only expands 0.0010" on subsequent shots. The net difference of not having to move the extra five ten-thousandths of an inch applies to a SAAMI .308 case diameter of .4539" at the shoulder is 34% less volume increase on the second shot because the cause was already expanded by .0005". So more energy goes out because less is absorbed by the case body. Obviously not perfect because the case is tapered and I pulled the radial clearance out of thin air, but it's my poor redneck attempt at describing exponential growth in the area of circles - relatively small increases in radius result in higher percentage increase in area because area grows at the square of the increase in radius. (engineers - don't cry at my poor math words)</p></blockquote><p></p>
[QUOTE="QuietTexan, post: 2192560, member: 116181"] Probably more to do with a higher portion of energy in the shot going to forming the full case body against the chamber. Especially if you aren't FL sizing going forward, the initial shot affects more brass than subsequent shots, especially if you don't FL size to a minimum spec going forward because most of the case is not sized down before subsequent shots. My thought process (with kind-of guessed at numbers): If the difference in the case and chamber is .0015", the case body moves .0015" radially on the initial shot. Let's say it springs back a full ".0010, it's .0005 larger than before, and then it then only expands 0.0010" on subsequent shots. The net difference of not having to move the extra five ten-thousandths of an inch applies to a SAAMI .308 case diameter of .4539" at the shoulder is 34% less volume increase on the second shot because the cause was already expanded by .0005". So more energy goes out because less is absorbed by the case body. Obviously not perfect because the case is tapered and I pulled the radial clearance out of thin air, but it's my poor redneck attempt at describing exponential growth in the area of circles - relatively small increases in radius result in higher percentage increase in area because area grows at the square of the increase in radius. (engineers - don't cry at my poor math words) [/QUOTE]
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Case weight variability question
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