Standard Deviation Relevance... ?

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  • Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    General rule of thumb is you want a SD of 15 for 600 yards, and 10 for 1000, over 22 shots.

    i've never seen this rule of thumb... why 15 instead of 16. sure its close but my point is.. if it's a rule of thumb, it came from somewhere.
     

    Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    For hunting, I would match my POA and POI for the cold bore shot. Or maybe split the difference between the 1st and 2nd shot.

    For long range match or similar, I would set POA and POI for when the {POI settles down. But document the POA to POI difference for the first couple shots to compensate.

    Hunting, I want the least things to think about for the first shot. So sight in for maximum point blank zero, POA = POI for first shot.

    At the range, I use 100 yard zero, distance charts, and can dial or hold off for first cold bore shot.

    I'm on the same page. I'll do a few more chronograph tests to see if the cold bore thing persists then set zero from that. It's... like building a relationship with the firearm i suppose.. how how far to go when shes cold.. and nice n hot.
     

    Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    I didn't take the time to run the numbers but, take that 1/2 MOA rifle shooting a 1.75" group and add the .7" difference in drop and you already have 2.45". Now, factor in a really good shooter with about a 1 MOA hold and you have 4.2". Pretty easy to miss a groundhog when optimal conditions give you only a 4.2" group, and that is without factoring in outside conditions like wind.

    I wasn't following your math for a moment but i'm with ya. I tested these off a bench using sandbangs (front and rear) just like i pop groundhogs.. off sandbags, front and rear. this gives me a 1/2 MOA group.

    I tend to get most of the groundhogs while they are prone (not standing up). So far, the only ones i miss are over 500y unless i'm using something over 100gr. though i haven't tested the 69 or 75 gr at that range yet.

    Dope sheet shows estimated drift w/ 10 mph wind at full value etc etc. Aim a smidge higher than normal if first shot.

    Also.. come to think of it.. most of the time i see a groundhog it's been a good 2-3 hours before he comes out.. barrel warming up in the sun. this test i just took the rifle out of the AC car and shot w/in 2 minutes.

    Might chronograph it again w/o the dramatic change in temp.. i love MDShooters!
     

    Park ranger

    Ultimate Member
    Dec 6, 2015
    2,315
    i've never seen this rule of thumb... why 15 instead of 16. sure its close but my point is.. if it's a rule of thumb, it came from somewhere.

    Rule if thumb and not hard facts because BC will determine how the shots will effect elevation. But, in theory, 15 won't leave the X ring but 16 will.

    Do you shoot NRA style high power?
     

    noylj

    Active Member
    Jun 3, 2012
    144
    If you are shooting at distances of 300 yds or greater, and you have two loads with "the same" accuracy, the lower SD will most likely be more accurate at long range. For most of us, SD is meaningless. It is the target that tells the tale. If the trajectory matters, then you will find that out by shooting at the longer distances and not by simply assuming the lower SD will be more accurate.
     

    Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    Rule if thumb and not hard facts because BC will determine how the shots will effect elevation. But, in theory, 15 won't leave the X ring but 16 will.

    Do you shoot NRA style high power?

    I do not. Paper to zero.. gongs for fun... deer and groundhogs... 100-550 yards.
     

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