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Tweaking bc’s
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<blockquote data-quote="Chase723" data-source="post: 2253054" data-attributes="member: 21524"><p>Couple things. This is all based on the assumption that your scope tracks perfect in addition to what has already been mentioned.</p><p></p><p> First, for velocity, the number you get from a chronograph is not absolute. Like has been mentioned, it's a starting point. Even a Magnetospeed being 99.5-99.9% accurate is going to give you a variance of 3-15fps in a 3000fps rifle. So it gets you really close but you need to true it based on your come ups before BC has a major effect. 500 yards is a great place to do this. 15fps doesn't seem like much but combine this with what I mentioned above and it easily accounts for your difference. Are you centered punching steel at 500? Or are you off .1-.2 mils? Don't discount that. The bullet never lies.</p><p></p><p>Second, there is always going to be some BC variation from barrel to barrel so once you true your velocity you need to true your BC at distance. Since you can shoot at 800, once you know all of the above is correct and you have tried your velocity, adjust your BC at 800 to match your come up. Then shoot at 300, 400, etc on out to make sure it all lines up.</p><p></p><p>Hint, if after adjusting your BC you now notice that your on target DOPE for targets at closer distances doesn't match up to the adjustments as indicated by your ballistics calculator then either your zero offset, scope height, velocity, or scope tracking, or a combination thereof, are not correct.</p></blockquote><p></p>
[QUOTE="Chase723, post: 2253054, member: 21524"] Couple things. This is all based on the assumption that your scope tracks perfect in addition to what has already been mentioned. First, for velocity, the number you get from a chronograph is not absolute. Like has been mentioned, it’s a starting point. Even a Magnetospeed being 99.5-99.9% accurate is going to give you a variance of 3-15fps in a 3000fps rifle. So it gets you really close but you need to true it based on your come ups before BC has a major effect. 500 yards is a great place to do this. 15fps doesn’t seem like much but combine this with what I mentioned above and it easily accounts for your difference. Are you centered punching steel at 500? Or are you off .1-.2 mils? Don’t discount that. The bullet never lies. Second, there is always going to be some BC variation from barrel to barrel so once you true your velocity you need to true your BC at distance. Since you can shoot at 800, once you know all of the above is correct and you have tried your velocity, adjust your BC at 800 to match your come up. Then shoot at 300, 400, etc on out to make sure it all lines up. Hint, if after adjusting your BC you now notice that your on target DOPE for targets at closer distances doesn’t match up to the adjustments as indicated by your ballistics calculator then either your zero offset, scope height, velocity, or scope tracking, or a combination thereof, are not correct. [/QUOTE]
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