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Rifles, Reloading, Optics, Equipment
Reloading
Great groups but not great SD
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<blockquote data-quote="RegionRat" data-source="post: 3093481" data-attributes="member: 57231"><p>I have a minute to burn and this is easy if you run these numbers all the time.</p><p></p><p>Let's assume Barnes 208 LRX at typical speeds for the 300 PRC are roughly 2950 fps</p><p></p><p>If the SD is 17, then there will be a probability distribution that says at +/- 2 sigma the ES is 68 fps, and at +/- 3 sigma the ES is 102 fps</p><p>Now if we back calculate the trajectory at 400 and 800 yards we will see the following drops with a 200 yard zero.</p><p></p><p>2950 fps 400 yards 4.1 MOA, 800 yards 15.5 MOA</p><p>+/- 2 sigma gives 3018 fps 400 yards 3.9 MOA, 800 yards 14.7 MOA</p><p>+/- 3 sigma gives 3052 fps 400 yards 3.8 MOA, 800 yards 14.3 MOA</p><p></p><p>So, the worst case is when you look at it over +/- 3 sigma where the change from the average means the velocity ES is as high as 102 fps, so the elevation change is worth (4.1-3.8)x4= 1.2" at 400 yards, and (15.5 - 14.3)x8= 9.6" at 800 yards.</p><p></p><p>So, with the SD at 17, your vertical dispersion at 800 yards would be roughly 9.6" at 800 yards from the speed variations alone.</p><p></p><p>The math shows the round is still hitting very hard at 800 yards, but ethically the dispersion and flight delay doesn't leave you much room for error.</p><p></p><p>If I were to give you some advice it would be to be honest with yourself about your shooting ability, which includes shooting under pressure, the odds the animal won't move, the range error, and the wind error, and the DOPE error due to cold bore and temperature changes. I would go out and test yourself against a clock and a 10" diameter target and see what you can do, and then decide if you need more time at the loading bench, or the range, or both.</p></blockquote><p></p>
[QUOTE="RegionRat, post: 3093481, member: 57231"] I have a minute to burn and this is easy if you run these numbers all the time. Let's assume Barnes 208 LRX at typical speeds for the 300 PRC are roughly 2950 fps If the SD is 17, then there will be a probability distribution that says at +/- 2 sigma the ES is 68 fps, and at +/- 3 sigma the ES is 102 fps Now if we back calculate the trajectory at 400 and 800 yards we will see the following drops with a 200 yard zero. 2950 fps 400 yards 4.1 MOA, 800 yards 15.5 MOA +/- 2 sigma gives 3018 fps 400 yards 3.9 MOA, 800 yards 14.7 MOA +/- 3 sigma gives 3052 fps 400 yards 3.8 MOA, 800 yards 14.3 MOA So, the worst case is when you look at it over +/- 3 sigma where the change from the average means the velocity ES is as high as 102 fps, so the elevation change is worth (4.1-3.8)x4= 1.2" at 400 yards, and (15.5 - 14.3)x8= 9.6" at 800 yards. So, with the SD at 17, your vertical dispersion at 800 yards would be roughly 9.6" at 800 yards from the speed variations alone. The math shows the round is still hitting very hard at 800 yards, but ethically the dispersion and flight delay doesn't leave you much room for error. If I were to give you some advice it would be to be honest with yourself about your shooting ability, which includes shooting under pressure, the odds the animal won't move, the range error, and the wind error, and the DOPE error due to cold bore and temperature changes. I would go out and test yourself against a clock and a 10" diameter target and see what you can do, and then decide if you need more time at the loading bench, or the range, or both. [/QUOTE]
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Great groups but not great SD
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