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Rifles, Reloading, Optics, Equipment
Reloading
OBT method, barrel length vs velocity
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<blockquote data-quote="Tripodmvr7" data-source="post: 1997539" data-attributes="member: 115545"><p>I have done more than 1000 calcs for shooters and would be interested in looking at your figures. </p><p></p><p>If you supply the following I can do a recalculation and vet the data.</p><p></p><p>1. Measured barrel length in mm as it is the easiest - use cleaning rod and measure from cocked bolt to muzzle tip.</p><p>2. COL as shot - QL needs from base to tip of bullet - jump allowed is helpful to see if bullet is jammed in the lands.</p><p>3. Bullet used - number on box is helpful.</p><p>4. Water case volume measured with fired case that has not been resized in any way - weight in grains is easiest. Weigh empty case and then fill with slightly soapy water till water is level at case mouth. Weigh again and difference is the case volume. Do five to get a mean and idea of variance.</p><p>5. Type of propellant and charge weight.</p><p>6. Speed obtained and what method - optic chronies I would need distance from muzzle - I advise 5m as muzzle blast sometimes gives false readings.</p><p></p><p>You have not stored any of the calcs that you have done? If so I can provide an email address and you can send them directly.</p><p></p><p>Below is an example of a calculated prediction. In practice the burning rate (BRF) at top right is normally higher and needs to be calibrated to actual speed achieved. COL and other relevant figures are defaults as supplied by the program. You can see that the barrel times have been matched as per the OBT theory.</p></blockquote><p></p>
[QUOTE="Tripodmvr7, post: 1997539, member: 115545"] I have done more than 1000 calcs for shooters and would be interested in looking at your figures. If you supply the following I can do a recalculation and vet the data. 1. Measured barrel length in mm as it is the easiest - use cleaning rod and measure from cocked bolt to muzzle tip. 2. COL as shot - QL needs from base to tip of bullet - jump allowed is helpful to see if bullet is jammed in the lands. 3. Bullet used - number on box is helpful. 4. Water case volume measured with fired case that has not been resized in any way - weight in grains is easiest. Weigh empty case and then fill with slightly soapy water till water is level at case mouth. Weigh again and difference is the case volume. Do five to get a mean and idea of variance. 5. Type of propellant and charge weight. 6. Speed obtained and what method - optic chronies I would need distance from muzzle - I advise 5m as muzzle blast sometimes gives false readings. You have not stored any of the calcs that you have done? If so I can provide an email address and you can send them directly. Below is an example of a calculated prediction. In practice the burning rate (BRF) at top right is normally higher and needs to be calibrated to actual speed achieved. COL and other relevant figures are defaults as supplied by the program. You can see that the barrel times have been matched as per the OBT theory. [/QUOTE]
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Rifles, Reloading, Optics, Equipment
Reloading
OBT method, barrel length vs velocity
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