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Rifles, Reloading, Optics, Equipment
Reloading
Brass weight discrepancies
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<blockquote data-quote="entoptics" data-source="post: 2321701" data-attributes="member: 104268"><p>Assuming the volume difference is entirely represented by the weight difference (not likely the case), brass is ~8X as dense as H2O or powder. So you're 23 grain difference in brass weight would only be 3-4 grains of powder <em><u>capacity</u></em>. The nominal 270 powder capacity it 67 grains H2O. So that's an ~5% difference in <em><u>capacity.</u></em></p><p></p><p>Thing is velocity (pressure) does not linearly change with capacity. On top of that, it will vary based on the burn rate of the powder used. It all relates to expansion volume. On a basic level, it's why you can get higher velocity out of a magnum cartridge at the same pressure, but to do that, you need to add more powder...</p><p></p><p>Anyway, I did some experiments awhile back. Though not nearly as extreme a difference as your situation, they may be helpful...</p><p></p><p>[URL unfurl="true"]https://www.longrangehunting.com/threads/quantitative-analysis-of-brass-volume-weight-and-velocity.255205/[/URL]</p><p></p><p>I did some other less rigorous testing on variable head stamped brass (308 and 556), and if I remember right, I was seeing a range of 1-4 fps per grain of brass weight. Take the middle of that, and you're looking at 40-50 fps for your situation. That's probably about 1 grain of powder in a 270 win.</p><p></p><p>If I were in your situation, I'd take the heavy brass and I'd load up 2 rounds each at -2, -1.5, and -1 grains and shoot them over a chrony. I'd bet you'll be near the light brass with 1-1.5 grains less powder in the heavy brass.</p></blockquote><p></p>
[QUOTE="entoptics, post: 2321701, member: 104268"] Assuming the volume difference is entirely represented by the weight difference (not likely the case), brass is ~8X as dense as H2O or powder. So you're 23 grain difference in brass weight would only be 3-4 grains of powder [I][U]capacity[/U][/I]. The nominal 270 powder capacity it 67 grains H2O. So that's an ~5% difference in [I][U]capacity.[/U][/I] Thing is velocity (pressure) does not linearly change with capacity. On top of that, it will vary based on the burn rate of the powder used. It all relates to expansion volume. On a basic level, it's why you can get higher velocity out of a magnum cartridge at the same pressure, but to do that, you need to add more powder... Anyway, I did some experiments awhile back. Though not nearly as extreme a difference as your situation, they may be helpful... [URL unfurl="true"]https://www.longrangehunting.com/threads/quantitative-analysis-of-brass-volume-weight-and-velocity.255205/[/URL] I did some other less rigorous testing on variable head stamped brass (308 and 556), and if I remember right, I was seeing a range of 1-4 fps per grain of brass weight. Take the middle of that, and you're looking at 40-50 fps for your situation. That's probably about 1 grain of powder in a 270 win. If I were in your situation, I'd take the heavy brass and I'd load up 2 rounds each at -2, -1.5, and -1 grains and shoot them over a chrony. I'd bet you'll be near the light brass with 1-1.5 grains less powder in the heavy brass. [/QUOTE]
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