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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
7MM RUM/WC872 and the chrony ...
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<blockquote data-quote="dwm" data-source="post: 27410" data-attributes="member: 1136"><p>Hey guys, I have some data here that doesn't quite make sense.</p><p></p><p>At the range yesterday I shot 5 - 5 shot groups with the 7MM RUM, 28 inch barrel, not counting muzzle break.</p><p></p><p>Here is the data:</p><p></p><p>New cases, full length sized with Redding FL bushing die (0.310). Cases neck turned to 0.013 thickness. Chamber has 0.312 neck.</p><p></p><p>Fed GM215M primers</p><p>WC872 powder, all charges weighed to +0.1 grains</p><p>Nosler 160 Accubond bullets</p><p></p><p>Temp: 91 degrees, 60-70% humidity, close to sea level.</p><p>Wind: 3-5 gusting to 10, straight into bench</p><p></p><p>Six fouling shots fired before this data was collected.</p><p></p><p>Barrel was allowed time to cool between each shot.</p><p></p><p>Group 1 - 98 grains (2 1/2 inch group)</p><p>3446</p><p>3416</p><p>3474</p><p>3458</p><p>3486</p><p></p><p>Group 2 - 98.5 grains (2 1/2 inch group)</p><p>3492</p><p>3567</p><p>3502</p><p>3454</p><p>3489</p><p></p><p>Group 3 - 99 grains (2 1/2 inch group)</p><p>3466</p><p>3539</p><p>3429</p><p>3541</p><p>3491</p><p></p><p>Group 4 - 99.5 grains (3 within 1/2 inch, other two low 1 inch in different directions.)</p><p>3484</p><p>3555</p><p>3454</p><p>3470</p><p>3452</p><p></p><p>Group 5 - 100 grains (2 inch group, 4 in the corners of 2 inches)</p><p>3483</p><p>3482</p><p>3482</p><p>3486</p><p>3510</p><p></p><p>No pressure signs at all, no marks on any cases, no sticky anything.</p><p></p><p>Why didn't the velocity change more?</p><p></p><p>Is WC872 really that slow burning that a 2 grain difference only made the velocity go up 30 feet per second?</p><p></p><p>Am I using enough neck tension?</p><p></p><p>Some not to good groups.</p><p></p><p>Doug</p></blockquote><p></p>
[QUOTE="dwm, post: 27410, member: 1136"] Hey guys, I have some data here that doesn't quite make sense. At the range yesterday I shot 5 - 5 shot groups with the 7MM RUM, 28 inch barrel, not counting muzzle break. Here is the data: New cases, full length sized with Redding FL bushing die (0.310). Cases neck turned to 0.013 thickness. Chamber has 0.312 neck. Fed GM215M primers WC872 powder, all charges weighed to +0.1 grains Nosler 160 Accubond bullets Temp: 91 degrees, 60-70% humidity, close to sea level. Wind: 3-5 gusting to 10, straight into bench Six fouling shots fired before this data was collected. Barrel was allowed time to cool between each shot. Group 1 - 98 grains (2 1/2 inch group) 3446 3416 3474 3458 3486 Group 2 - 98.5 grains (2 1/2 inch group) 3492 3567 3502 3454 3489 Group 3 - 99 grains (2 1/2 inch group) 3466 3539 3429 3541 3491 Group 4 - 99.5 grains (3 within 1/2 inch, other two low 1 inch in different directions.) 3484 3555 3454 3470 3452 Group 5 - 100 grains (2 inch group, 4 in the corners of 2 inches) 3483 3482 3482 3486 3510 No pressure signs at all, no marks on any cases, no sticky anything. Why didn't the velocity change more? Is WC872 really that slow burning that a 2 grain difference only made the velocity go up 30 feet per second? Am I using enough neck tension? Some not to good groups. Doug [/QUOTE]
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7MM RUM/WC872 and the chrony ...
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