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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
What “Causes” a Low SD/ES?
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<blockquote data-quote="jakeSCH" data-source="post: 2260282" data-attributes="member: 119202"><p>Low ES / SD is caused by repeating exact same pressure curve with the exact same bullet shape / material / weight.</p><p></p><p>Things that help this</p><p>- Powder mass (repeatable down to the kernal)</p><p>- Brass internal volume (some do this by weight sorting brass w/ exact headspace)</p><p>- Consistent neck tension (crimp helps as well)</p><p>- Consistent ignition (uniform flash holes, primer seating depth)</p><p></p><p>There are other things but those help the "most". When you find a "node", you are now timing your bullet to exit the barrel at a maximum deflection (up or down). Think of a sine wave with the bullet exiting at peak or valley. Doing this provides forgiveness in being off in the other areas above because the duration of the barrel in that position is slightly longer than not in a node. This is most likely what you experienced by moving up 0.3 grains, you left a peak / valley.</p><p></p><p>Nodes are great, but I've put 10 rounds within 2 fps without being on a node but that costs a lot more money with expensive scales.</p></blockquote><p></p>
[QUOTE="jakeSCH, post: 2260282, member: 119202"] Low ES / SD is caused by repeating exact same pressure curve with the exact same bullet shape / material / weight. Things that help this - Powder mass (repeatable down to the kernal) - Brass internal volume (some do this by weight sorting brass w/ exact headspace) - Consistent neck tension (crimp helps as well) - Consistent ignition (uniform flash holes, primer seating depth) There are other things but those help the "most". When you find a "node", you are now timing your bullet to exit the barrel at a maximum deflection (up or down). Think of a sine wave with the bullet exiting at peak or valley. Doing this provides forgiveness in being off in the other areas above because the duration of the barrel in that position is slightly longer than not in a node. This is most likely what you experienced by moving up 0.3 grains, you left a peak / valley. Nodes are great, but I've put 10 rounds within 2 fps without being on a node but that costs a lot more money with expensive scales. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
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What “Causes” a Low SD/ES?
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