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Long Range Hunting & Shooting
.300 Winchester Magum Bullet Choice - Expanded
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<blockquote data-quote="Jon A" data-source="post: 95327" data-attributes="member: 319"><p>Interesting, Marc. 47"--yikes! I guess that's why we actually shoot at these ranges to confirm the charts. /ubbthreads/images/graemlins/wink.gif</p><p></p><p>You don't happen to be using a really, really slow twist do you? Other than that I think there must be some other error (or combination of more than one) to cause the discrepancy--in other words the BC of the bullet isn't entirely to blame.</p><p></p><p>Even Rick's data you posted shows the bullet doing much better. I measured the 200 AB at .550 and I'm confident that's a good, conservative number if anything as Brent Moffit here has also measured it numerous times higher than that--right up close to advertised. So if you scale Rick's data to that known control, his measurement of the 180 BT goes to .497 even using my conservative number for the AB. Trust me, if he measured the Berger he wouldn't get anywhere close to .640, it would be low just like all the rest.</p><p></p><p>I know many are happy once they have actual firing results and quit there but I'm too anal I guess. /ubbthreads/images/graemlins/wink.gif I'm happier when I can find out exactly <em>why</em> the computer was wrong. It always comes down to me putting some garbage in.</p><p></p><p>The first thing I'd double check is the muzzle velocity. My 20 yr old Pro-Tach chronograph has served me well over the years, but it wasn't uncommon at all--especially under "funny" light conditions--for it to give me whacky readings. Sometimes 200-300 fps too high. But they'd be consistent and give me an average that was that high. </p><p></p><p>If I had believed those velocities and adjusted the BC in the program to match the actual trajectory I would have had to put in about .3 for some bullets. Two wrongs added to get the right answer.</p><p></p><p>That's why I just ordered my second Oehler. Getting a really accurate MV is highly important. So I'd try and shoot that load over another chronograph to see if that MV wasn't a bit optimistic. It happens, and if off far enough that could explain most of the difference by itself.</p><p></p><p>Then I'd measure the click value. If it was really only, say, .95" at 100 that might go unnoticed but could mean quite an error out at 1000. And of course, when things aren't adding up the 100 yd zero should always be re-checked. Sometimes scopes just don't track right and you find the error there.</p><p></p><p>Then there are conditions. If you were using a barometer, you might want to check it against another, etc. The weather can easily shift the density altitude close to 1000 ft without your noticing unless you're measuring. Enough to make a significant difference at 1000 yds.</p><p></p><p>These things or a combination could easily cause the required 31.5 SMOA. If it was more of an unknown bullet I'd be more likely to blame the BC but I really think we have enough data to show that this one's BC shouldn't be that low, and if you need to enter it that low in the program to make it match the real world, I really think it must be compensating for some bad data entered elsewhere.</p><p></p><p>Anyway, good luck.</p></blockquote><p></p>
[QUOTE="Jon A, post: 95327, member: 319"] Interesting, Marc. 47"--yikes! I guess that's why we actually shoot at these ranges to confirm the charts. [img]/ubbthreads/images/graemlins/wink.gif[/img] You don't happen to be using a really, really slow twist do you? Other than that I think there must be some other error (or combination of more than one) to cause the discrepancy--in other words the BC of the bullet isn't entirely to blame. Even Rick's data you posted shows the bullet doing much better. I measured the 200 AB at .550 and I'm confident that's a good, conservative number if anything as Brent Moffit here has also measured it numerous times higher than that--right up close to advertised. So if you scale Rick's data to that known control, his measurement of the 180 BT goes to .497 even using my conservative number for the AB. Trust me, if he measured the Berger he wouldn't get anywhere close to .640, it would be low just like all the rest. I know many are happy once they have actual firing results and quit there but I'm too anal I guess. [img]/ubbthreads/images/graemlins/wink.gif[/img] I'm happier when I can find out exactly [i]why[/i] the computer was wrong. It always comes down to me putting some garbage in. The first thing I'd double check is the muzzle velocity. My 20 yr old Pro-Tach chronograph has served me well over the years, but it wasn't uncommon at all--especially under "funny" light conditions--for it to give me whacky readings. Sometimes 200-300 fps too high. But they'd be consistent and give me an average that was that high. If I had believed those velocities and adjusted the BC in the program to match the actual trajectory I would have had to put in about .3 for some bullets. Two wrongs added to get the right answer. That's why I just ordered my second Oehler. Getting a really accurate MV is highly important. So I'd try and shoot that load over another chronograph to see if that MV wasn't a bit optimistic. It happens, and if off far enough that could explain most of the difference by itself. Then I'd measure the click value. If it was really only, say, .95" at 100 that might go unnoticed but could mean quite an error out at 1000. And of course, when things aren't adding up the 100 yd zero should always be re-checked. Sometimes scopes just don't track right and you find the error there. Then there are conditions. If you were using a barometer, you might want to check it against another, etc. The weather can easily shift the density altitude close to 1000 ft without your noticing unless you're measuring. Enough to make a significant difference at 1000 yds. These things or a combination could easily cause the required 31.5 SMOA. If it was more of an unknown bullet I'd be more likely to blame the BC but I really think we have enough data to show that this one's BC shouldn't be that low, and if you need to enter it that low in the program to make it match the real world, I really think it must be compensating for some bad data entered elsewhere. Anyway, good luck. [/QUOTE]
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