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Long Range Hunting & Shooting
Necessary precision to kill something
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<blockquote data-quote="LRNut" data-source="post: 3060644" data-attributes="member: 3230"><p>No, it doesn't make any sense at all. Let's assume bullet groups are normally distributed. I shoot a three shot group where two land dead center and one is 1/4 MOA from dead center (the best possible 3 shot group that is 1/4 MOA). I have a 1/4 MOA group. However, the standard deviation for this is .144, which means, based on this extremely small sample, that 68% of my future shots will land plus or minus .144, which creates a group size of .288 MOA. Close enough for government work; let's call that 1/4 MOA. But that is only 68% of fired bullets. 90% will land within .23 MOA of center (.46 MOA). Nearly all, or 99%, will land plus or minus .432" from dead center, or close to the dreaded MOA rifle (.864").</p><p></p><p>Let's suppose you can call the wind within 1 mph and your wind drift is 4" [USER=69648]@1000 yards[/USER] per mile of wind. 68% of the time you are going to hit the deer simply because 68% of your bullets are within 1.44" of dead center. 10% of your shots are going to hit at least .25 MOA from dead center, which means half are going to miss due to wind. I am not factoring in wind that changes during TOF or between your wind call and the trigger pull. If your wind call is off by 2 mph, your entire group is displaced 8" or nearly the entire kill zone of a deer. Still half the time you kill it because half your bullets are hitting left or right of dead center. The "fringe" of the group, the 2" that is still on target gives you a few more percent chance of a it. Pretty close to the odds the podcaster revealed. And to his point, that is why wind call skills are far more important than accuracy.</p><p></p><p>Now suppose another rifle shoots a 30 shot group that measures .4 MOA (almost double your group size!). You might think your rifle is the better LR weapon - after all, yours is 1/4 MOA. But let's suppose of those thirty shots, 5 hit dead center, 20 hit .1 MOA from center, and 5 hit .2 MOA from dead center. The standard deviation of those 30 is .063. That means 68% of our shots will land in a .12 group. 99% will land in a .378 group (less than 1/2 MOA but almost identical to our 30 shot group). Which rifle do you want now? The 1/4 MOA 3 shot or the 30 shot .4 MOA?</p><p></p><p>Incidentally, with the 1/4 MOA (3 shot group) rifle you need to call the wind within .17 mph to hit 99% of the time; with the 30 shot .4 MOA rifle your allowable with error (99% hit rate) increases to .77 mph. (Deer at 1000 yards with a 10" vital area.)</p><p></p><p>Hopefully this illustrates the point in the podcast that 3 shot 1/4 MOA groups don't translate into much in real life.</p></blockquote><p></p>
[QUOTE="LRNut, post: 3060644, member: 3230"] No, it doesn't make any sense at all. Let's assume bullet groups are normally distributed. I shoot a three shot group where two land dead center and one is 1/4 MOA from dead center (the best possible 3 shot group that is 1/4 MOA). I have a 1/4 MOA group. However, the standard deviation for this is .144, which means, based on this extremely small sample, that 68% of my future shots will land plus or minus .144, which creates a group size of .288 MOA. Close enough for government work; let's call that 1/4 MOA. But that is only 68% of fired bullets. 90% will land within .23 MOA of center (.46 MOA). Nearly all, or 99%, will land plus or minus .432" from dead center, or close to the dreaded MOA rifle (.864"). Let's suppose you can call the wind within 1 mph and your wind drift is 4" [USER=69648]@1000 yards[/USER] per mile of wind. 68% of the time you are going to hit the deer simply because 68% of your bullets are within 1.44" of dead center. 10% of your shots are going to hit at least .25 MOA from dead center, which means half are going to miss due to wind. I am not factoring in wind that changes during TOF or between your wind call and the trigger pull. If your wind call is off by 2 mph, your entire group is displaced 8" or nearly the entire kill zone of a deer. Still half the time you kill it because half your bullets are hitting left or right of dead center. The "fringe" of the group, the 2" that is still on target gives you a few more percent chance of a it. Pretty close to the odds the podcaster revealed. And to his point, that is why wind call skills are far more important than accuracy. Now suppose another rifle shoots a 30 shot group that measures .4 MOA (almost double your group size!). You might think your rifle is the better LR weapon - after all, yours is 1/4 MOA. But let's suppose of those thirty shots, 5 hit dead center, 20 hit .1 MOA from center, and 5 hit .2 MOA from dead center. The standard deviation of those 30 is .063. That means 68% of our shots will land in a .12 group. 99% will land in a .378 group (less than 1/2 MOA but almost identical to our 30 shot group). Which rifle do you want now? The 1/4 MOA 3 shot or the 30 shot .4 MOA? Incidentally, with the 1/4 MOA (3 shot group) rifle you need to call the wind within .17 mph to hit 99% of the time; with the 30 shot .4 MOA rifle your allowable with error (99% hit rate) increases to .77 mph. (Deer at 1000 yards with a 10" vital area.) Hopefully this illustrates the point in the podcast that 3 shot 1/4 MOA groups don't translate into much in real life. [/QUOTE]
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