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Hunting
Long Range Hunting & Shooting
Different State - POI Change....is this normal?
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<blockquote data-quote="HiTechRob" data-source="post: 1633905" data-attributes="member: 71328"><p>Well, depending on the powder you are using, you can see a 1.5 fps to 3.5 fps variance in muzzle velocity in the same direction as your temperature change from zero. I see very little change using the Hodgdon Extreme powders like H1000 and Retumbo. For example, if the temperature went from 80F to 40F, then 40 x 1.5 = 60 fps decrease in MV up to 40 x 3.5 = 140 fps. That definitely will create a bullet impact change on the target and explains that you were low.... 1 inch low seems a bit much though. Also, a 2,100-foot increase in altitude, assuming pressure and humidity are constant, would negate that drop somewhat as the less dense the air is the less drag on the bullet and thus less drop you would have. What direction (N, S, E, W) you zeroed the rifle vs. the direction you shot can make a difference - but not at 100 yards... I shoot a 7RM as well but mainly shoot a 168-grain Berger VLD-H. It doesn't move much and my ballistic calculator is hooked up to my Kestrel wind meter to account for the change in zero environmentals vs. my current environmentals in my hunt area.</p></blockquote><p></p>
[QUOTE="HiTechRob, post: 1633905, member: 71328"] Well, depending on the powder you are using, you can see a 1.5 fps to 3.5 fps variance in muzzle velocity in the same direction as your temperature change from zero. I see very little change using the Hodgdon Extreme powders like H1000 and Retumbo. For example, if the temperature went from 80F to 40F, then 40 x 1.5 = 60 fps decrease in MV up to 40 x 3.5 = 140 fps. That definitely will create a bullet impact change on the target and explains that you were low.... 1 inch low seems a bit much though. Also, a 2,100-foot increase in altitude, assuming pressure and humidity are constant, would negate that drop somewhat as the less dense the air is the less drag on the bullet and thus less drop you would have. What direction (N, S, E, W) you zeroed the rifle vs. the direction you shot can make a difference - but not at 100 yards... I shoot a 7RM as well but mainly shoot a 168-grain Berger VLD-H. It doesn't move much and my ballistic calculator is hooked up to my Kestrel wind meter to account for the change in zero environmentals vs. my current environmentals in my hunt area. [/QUOTE]
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Different State - POI Change....is this normal?
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