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Rifles, Reloading, Optics, Equipment
Reloading
New Reloading Method for me
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<blockquote data-quote="nicholasjohn" data-source="post: 1910388" data-attributes="member: 109113"><p>I've found that the pressure ring on the case body is slightly bigger around than the case head is just ahead of the extractor groove. ( So is the rim.) If I use a regular micrometer, I'm not really measuring the case head diameter. What is being is measured is the expanded case WALLS. How do you get around measuring that diameter, and get a clean measurement of the case head diameter ? </p><p></p><p>I use a blade micrometer, C-clamped to a table top, and stand the cartridge case on a flat piece of steel that elevates the case off the table just enough to put it between the blades at a repeatable height each time. I also mark each case, so that I'm measuring the same spot around its circumference that was measured before firing. ( Most cases aren't perfectly round, nor do they all measure the same size.) This is providing repeatable results, but it is sure a lot of monkeying around to do so. I haven't yet found a way to do this more handily, and still get good measurements. </p><p></p><p>There's a detailed write-up about this process in Nick Harvey's Practical Reloading Manual. He stresses the importance of using a case that has not been fired ( and work-hardened ) for making these measurements. He also recommends filing a flat spot on two opposing sides of the rim of the case, so that it won't interfere with the micrometer posts. ( This negates the need for the blade micrometer.) While this enables the accurate measurement of the largest diameter of the case head, it pretty much ruins the case for further use. </p><p></p><p>Lastly, what do these measurements mean ? Dave Skovill did a study years ago, with a wildcat cartridge based on the 9.3 X 62mm cartridge, which is very similar dimensionally to the 30-06 case at the head end. He did actual pressure measurements of his loads, as well as case head measurements, to see how they coincided. As I recall, .0005" of expansion at the case head coincided with 60,000 PSI with extreme regularity. He showed other values as well, and I have found that most factory loads on the 30-06 case head cartridges expanded .0003" in my rifles. I use .0005" as maximum for my use, and have been doing this for a couple of decades without any trouble. I may be leaving something on the table for velocity, but I have never stuck a case in a chamber. At this level of expansion, I have also gotten a little bit better than advertised factory load velocities - usually 50 to 60 fps. The only thing I really don't like about this process is that it is very tedious, and it's difficult to do on cold days.</p></blockquote><p></p>
[QUOTE="nicholasjohn, post: 1910388, member: 109113"] I've found that the pressure ring on the case body is slightly bigger around than the case head is just ahead of the extractor groove. ( So is the rim.) If I use a regular micrometer, I'm not really measuring the case head diameter. What is being is measured is the expanded case WALLS. How do you get around measuring that diameter, and get a clean measurement of the case head diameter ? I use a blade micrometer, C-clamped to a table top, and stand the cartridge case on a flat piece of steel that elevates the case off the table just enough to put it between the blades at a repeatable height each time. I also mark each case, so that I'm measuring the same spot around its circumference that was measured before firing. ( Most cases aren't perfectly round, nor do they all measure the same size.) This is providing repeatable results, but it is sure a lot of monkeying around to do so. I haven't yet found a way to do this more handily, and still get good measurements. There's a detailed write-up about this process in Nick Harvey's Practical Reloading Manual. He stresses the importance of using a case that has not been fired ( and work-hardened ) for making these measurements. He also recommends filing a flat spot on two opposing sides of the rim of the case, so that it won't interfere with the micrometer posts. ( This negates the need for the blade micrometer.) While this enables the accurate measurement of the largest diameter of the case head, it pretty much ruins the case for further use. Lastly, what do these measurements mean ? Dave Skovill did a study years ago, with a wildcat cartridge based on the 9.3 X 62mm cartridge, which is very similar dimensionally to the 30-06 case at the head end. He did actual pressure measurements of his loads, as well as case head measurements, to see how they coincided. As I recall, .0005" of expansion at the case head coincided with 60,000 PSI with extreme regularity. He showed other values as well, and I have found that most factory loads on the 30-06 case head cartridges expanded .0003" in my rifles. I use .0005" as maximum for my use, and have been doing this for a couple of decades without any trouble. I may be leaving something on the table for velocity, but I have never stuck a case in a chamber. At this level of expansion, I have also gotten a little bit better than advertised factory load velocities - usually 50 to 60 fps. The only thing I really don't like about this process is that it is very tedious, and it's difficult to do on cold days. [/QUOTE]
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New Reloading Method for me
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