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Rifles, Reloading, Optics, Equipment
Reloading
Brass weight... How important?
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<blockquote data-quote="entoptics" data-source="post: 1629959" data-attributes="member: 104268"><p>It's not surprising that the example you showed didn't establish a good correlation. I put all your data into excel, and did a few calculations. The extreme spread in your brass weight was 1 grain. The extreme spread in your water weights was 0.22 grains. The extreme spread in primer weights (not to mention variable powder residue if the brass weren't cleaned), was 0.06 grains.</p><p></p><p>Brass has a density of ~8 times that of powder or water. Therefore, a grain of brass volume = 0.125 gr of powder or water.</p><p></p><p>Assuming that the exact same amount of water volume ingresses into the primer, and the differences in weight were solely due to more or less brass, the primer variation alone would equate to 0.06*8 = 0.48 grains of H2O.</p><p></p><p>I applaud your efforts, and it's good science, but relative to the OP, you're putting a pretty fine edge on the question. I think the experiment would have different results if the variation being explored was much greater than the measuring tools' ability to resolve...</p><p></p><p>For ideally external dimension cases, a 1.6 grain spread in brass equals a 0.2 gr spread in powder volume, which for a 300 RUM is approximately 0.2% of the powder charge and/or H2O capacity.</p><p></p><p>A typical 26", 30 cal barrel ought to have a volume of ~450 gr of H2O, making the total expansion volume for burning powder about 550 gr of H2O in a 300 RUM.</p><p></p><p>Think about that. To change overall expansion volume in a 26" 300 RUM by 1% you'd need to see 44 grains of case variation.</p><p></p><p>All that being said, extreme weight variation in brass (greater than a few percent relative to the case weight), is likely an indicator of mediocre or poor brass quality, and therefore might affect precision for reasons unrelated to case volume.</p><p></p><p>Anyway IMO, if external dimensions are consistent, brass weight correlates to powder weight by a factor of ~8, and expansion volume (the real issue of concern) by a factor of ~10-100 depending on barrel length and caliber (short small bore has more affect than long big bore). If all your cases are within a couple of grains of each other, it's unlikely you're going to see much benefit in weight sorting.</p></blockquote><p></p>
[QUOTE="entoptics, post: 1629959, member: 104268"] It's not surprising that the example you showed didn't establish a good correlation. I put all your data into excel, and did a few calculations. The extreme spread in your brass weight was 1 grain. The extreme spread in your water weights was 0.22 grains. The extreme spread in primer weights (not to mention variable powder residue if the brass weren't cleaned), was 0.06 grains. Brass has a density of ~8 times that of powder or water. Therefore, a grain of brass volume = 0.125 gr of powder or water. Assuming that the exact same amount of water volume ingresses into the primer, and the differences in weight were solely due to more or less brass, the primer variation alone would equate to 0.06*8 = 0.48 grains of H2O. I applaud your efforts, and it's good science, but relative to the OP, you're putting a pretty fine edge on the question. I think the experiment would have different results if the variation being explored was much greater than the measuring tools' ability to resolve... For ideally external dimension cases, a 1.6 grain spread in brass equals a 0.2 gr spread in powder volume, which for a 300 RUM is approximately 0.2% of the powder charge and/or H2O capacity. A typical 26", 30 cal barrel ought to have a volume of ~450 gr of H2O, making the total expansion volume for burning powder about 550 gr of H2O in a 300 RUM. Think about that. To change overall expansion volume in a 26" 300 RUM by 1% you'd need to see 44 grains of case variation. All that being said, extreme weight variation in brass (greater than a few percent relative to the case weight), is likely an indicator of mediocre or poor brass quality, and therefore might affect precision for reasons unrelated to case volume. Anyway IMO, if external dimensions are consistent, brass weight correlates to powder weight by a factor of ~8, and expansion volume (the real issue of concern) by a factor of ~10-100 depending on barrel length and caliber (short small bore has more affect than long big bore). If all your cases are within a couple of grains of each other, it's unlikely you're going to see much benefit in weight sorting. [/QUOTE]
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Brass weight... How important?
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