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Rifles, Reloading, Optics, Equipment
Reloading
300 RUM load development questions
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<blockquote data-quote="Bart B" data-source="post: 779715" data-attributes="member: 5302"><p>Your chamber headspace is probably somewhere between the 2.4742" and 2.4842" dimensions shown in the following:</p><p></p><p><a href="http://www.saami.org/PubResources/CC_Drawings/Rifle/300%20Remington%20Ultra%20Magnum.pdf" target="_blank">http://www.saami.org/PubResources/CC_Drawings/Rifle/300 Remington Ultra Magnum.pdf</a></p><p></p><p>It doesn't matter what it is as all you need to do is set fired case shoulders back about .002". If you want to know what it actually is, you might need a chamber headspace GO gauge to calibrate your measureing tool, then compare fired case headspace to that. With max loads, the fired case headspace will typically be .001" to .002" shorter than actual chamber headspace. Without an adjustable chamber headspace gauge or set of gauges in .001" increments, it's gonna be a task to see exactly what it is.</p><p></p><p>What dimension is longer? Case length which is spec'd between 2.830" to 2.850" or case headspace which is spec'd between 2.4742" and 2.4842"?</p><p></p><p>Cases typically get longer (head to mouth) after each shoot and reesize cycle; it's the nature of the beast. How much depends on the diameter differences between case and chamber; the difference in your chamber and die diameters effect this; a greater difference means more case lengthening with each cycle. Some of the change is caused by how much the fired case shoulder's set back each time; minimal setback reduces the case growth when full length sized.</p><p> </p><p>With the extra slower powders, oft times max loads don't shoot as accurate as those powders a bit faster. And rarely does the powder producing the most muzzle velocity at max pressure specs shoot bullets as accurate as a slightly faster powder shooting bullets out 50 to 75 fps slower. The velocity vs. accuracy compromise issue may have settled in your domain.</p></blockquote><p></p>
[QUOTE="Bart B, post: 779715, member: 5302"] Your chamber headspace is probably somewhere between the 2.4742" and 2.4842" dimensions shown in the following: [url]http://www.saami.org/PubResources/CC_Drawings/Rifle/300%20Remington%20Ultra%20Magnum.pdf[/url] It doesn't matter what it is as all you need to do is set fired case shoulders back about .002". If you want to know what it actually is, you might need a chamber headspace GO gauge to calibrate your measureing tool, then compare fired case headspace to that. With max loads, the fired case headspace will typically be .001" to .002" shorter than actual chamber headspace. Without an adjustable chamber headspace gauge or set of gauges in .001" increments, it's gonna be a task to see exactly what it is. What dimension is longer? Case length which is spec'd between 2.830" to 2.850" or case headspace which is spec'd between 2.4742" and 2.4842"? Cases typically get longer (head to mouth) after each shoot and reesize cycle; it's the nature of the beast. How much depends on the diameter differences between case and chamber; the difference in your chamber and die diameters effect this; a greater difference means more case lengthening with each cycle. Some of the change is caused by how much the fired case shoulder's set back each time; minimal setback reduces the case growth when full length sized. With the extra slower powders, oft times max loads don't shoot as accurate as those powders a bit faster. And rarely does the powder producing the most muzzle velocity at max pressure specs shoot bullets as accurate as a slightly faster powder shooting bullets out 50 to 75 fps slower. The velocity vs. accuracy compromise issue may have settled in your domain. [/QUOTE]
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300 RUM load development questions
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