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Rifles, Reloading, Optics, Equipment
Rifles, Bullets, Barrels & Ballistics
Experiment for quantifying lot to lot variations of powders
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<blockquote data-quote="Bart B" data-source="post: 684933" data-attributes="member: 5302"><p>Interesting information, but I'm not surprized at the results. Watched a test comparing Sierra's 30 caliber 190-gr. HPMK's to Berger's 30 caliber 185-gr. VLD's in velocity tests at 5 and 997 yards. With both bullets at the same speeds around 2550 fps from the same barrel at 5 yards, the Sierra's went through the 997 yard screens about 40 fps faster than the Bergers. Why 997 yards? The down range screens were centered a couple yards in front of the 1000-yard targets atop the safety berm. A velocity test between the different 30 caliber 155's would be very easy to do the same way as this one was. That would best show which bullet had the highest BC over 997 yards, but the exact numbers wouldn't be known. Calculations from timing flight in different velocity bands ends up with a BC that's close, but actual speed differences down range gives the best comparisons.</p><p></p><p>In the above tests, down range screens were two sheets of aluminum foil covered 1/4" thick foam boards about 3 or 4 feet square. Spacing was 6 feet as I remember. The front and back foil sheets of each one were connected to the start and stop inputs on the down range chronograph. As bullets passed through each one, they connected the two foil layers triggering the chrono's timing circuits. There was some talk about one bullet being slowed down more than the other as it passed through the foam boards due to its nose shape and weight and that might induce an error in screen to screen timing. No conclusions were made as far as I know. But an interesting way to chronograph speeds a long ways away.</p><p></p><p>'Twould be interesting to see accuracy tests with both 155's at 1000 yards with 3 different lots of each bullets shot in 100-round test groups from 3 different barrels mounted in action-clamped rail guns. Meanwhile, we have to accept whatever one gets with each one in shoulder fired tests with few-shot groups. Note also that Sierra's new Palma 155 has a higher BC than their original one.</p></blockquote><p></p>
[QUOTE="Bart B, post: 684933, member: 5302"] Interesting information, but I'm not surprized at the results. Watched a test comparing Sierra's 30 caliber 190-gr. HPMK's to Berger's 30 caliber 185-gr. VLD's in velocity tests at 5 and 997 yards. With both bullets at the same speeds around 2550 fps from the same barrel at 5 yards, the Sierra's went through the 997 yard screens about 40 fps faster than the Bergers. Why 997 yards? The down range screens were centered a couple yards in front of the 1000-yard targets atop the safety berm. A velocity test between the different 30 caliber 155's would be very easy to do the same way as this one was. That would best show which bullet had the highest BC over 997 yards, but the exact numbers wouldn't be known. Calculations from timing flight in different velocity bands ends up with a BC that's close, but actual speed differences down range gives the best comparisons. In the above tests, down range screens were two sheets of aluminum foil covered 1/4" thick foam boards about 3 or 4 feet square. Spacing was 6 feet as I remember. The front and back foil sheets of each one were connected to the start and stop inputs on the down range chronograph. As bullets passed through each one, they connected the two foil layers triggering the chrono's timing circuits. There was some talk about one bullet being slowed down more than the other as it passed through the foam boards due to its nose shape and weight and that might induce an error in screen to screen timing. No conclusions were made as far as I know. But an interesting way to chronograph speeds a long ways away. 'Twould be interesting to see accuracy tests with both 155's at 1000 yards with 3 different lots of each bullets shot in 100-round test groups from 3 different barrels mounted in action-clamped rail guns. Meanwhile, we have to accept whatever one gets with each one in shoulder fired tests with few-shot groups. Note also that Sierra's new Palma 155 has a higher BC than their original one. [/QUOTE]
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Experiment for quantifying lot to lot variations of powders
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