Standard Deviation Relevance... ?

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  • Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    I’ve been using OCW loading sets instead of the traditional ladder sets but my question goes for both I assume. How much relevance do you throw into STD Dev?

    Is 12 tolerable for you if the groups are good or do you prefer an “okay group” with a lower dev?

    I’ve been leaning toward hotter/higher accuracy node and ignoring std dev for the most part but this one is right up there in std dev compared to my other rifles like 300win mag load for example has std dev of 12.


    0d191b77cf62b1245735df8e6fff390e.jpg



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    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    If you have an accurate load, without vertical stringing, why worry about the SD?

    The SD is one tool in finding that accurate load, but not the be all to end all.
     

    Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    And it looks like your major outlier was the first shot. Was that a cold bore?



    Yes it was. That’s why I write them down. I TYPICALLY take out the first and last shot but, in a hunting application ... the first shot is the one that matters most so I still document it.


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    dist1646

    Ultimate Member
    May 1, 2012
    8,758
    Eldersburg
    Looks like the difference between high and low in 195 fps, even if the first shot is discounted, there is still a 67 fps difference between high and low! You should definitely be able to get those numbers a lot closer.
     

    Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    Looks like the difference between high and low in 195 fps, even if the first shot is discounted, there is still a 67 fps difference between high and low! You should definitely be able to get those numbers a lot closer.

    i probably could but at what gain/benefit? This isn't for match shooting or anything CRITICAL to be spot on 100%. This round is for gongs and groundhogs out to 350 yards.

    It could be a ton of things, damaged chronogrpah.. 0.09 grains of powder more/less.... crim strength etc etc. but.. if the extreme spread is 0 what do i gain out of it? 1 inch of improved accuracy at 300 yards? i'm just guessing because i really have no idea. i guess i could put the numbers into a ballistic calculator and see what the drop is on extreme high vs low.. but i dont think the groundhog is going to care too.

    I value the feedback but fail to see WHY it's a critical number. YOu got me thinking though.. i'm going to look at the trajectory difference for high vs low.
     

    Moorvogi

    Firearm Advocate
    Dec 28, 2014
    855
    I value the feedback but fail to see WHY it's a critical number. YOu got me thinking though.. i'm going to look at the trajectory difference for high vs low.

    0.7 inches of drop difference at 350 yards between slowest to fastest bullet.

    YES, it makes a difference if i'm trimming the nut hair off a gnat at 100 yards but it's not going to make a difference for my application.

    The good news is, this goes for STD DEV too.. pick middle of the row and now were're about 0.4 +/- at 350 yards. I can deal with that groundhogs cant though HAHAH.
     

    hoppes-no9

    Member
    Nov 17, 2014
    19
    In my experience, a high SD load is less likely to be accurate. But there are no hard and fast rules -- a low SD load can be inaccurate, and a high SD load can be really accurate.

    It's fun to measure the SD and interesting to see how it changes as you get towards the hotter end (usually) but ultimately once a load is "fast enough" I go by the target not the SD.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    0.7 inches of drop difference at 350 yards between slowest to fastest bullet.

    YES, it makes a difference if i'm trimming the nut hair off a gnat at 100 yards but it's not going to make a difference for my application.

    The good news is, this goes for STD DEV too.. pick middle of the row and now were're about 0.4 +/- at 350 yards. I can deal with that groundhogs cant though HAHAH.

    In THEORY.

    But if the load is not showing a 3/4" vertical spread, then who cares?

    Case the numbers if you want, but it the load shoots a small group, it is accurate.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    Yes it was. That’s why I write them down. I TYPICALLY take out the first and last shot but, in a hunting application ... the first shot is the one that matters most so I still document it.

    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.
     

    Seabee

    Old Timer
    Oct 9, 2011
    517
    Left marylandistan to NC
    Neck tension was the biggest problem for me and getting numbers and groups to line up. Retired my old brass and began anew. The bullet seating effort was very noticeable between cases. Annealing helped but wasn't a cure.
     

    dist1646

    Ultimate Member
    May 1, 2012
    8,758
    Eldersburg
    0.7 inches of drop difference at 350 yards between slowest to fastest bullet.

    YES, it makes a difference if i'm trimming the nut hair off a gnat at 100 yards but it's not going to make a difference for my application.

    The good news is, this goes for STD DEV too.. pick middle of the row and now were're about 0.4 +/- at 350 yards. I can deal with that groundhogs cant though HAHAH.

    That is .7 just for the load difference. Now factor in the level of accuracy the rifle is capable of, then add in shooters error and that .7 rapidly becomes a miss. Something to think about.
     

    Pinecone

    Ultimate Member
    MDS Supporter
    Feb 4, 2013
    28,175
    That is .7 just for the load difference. Now factor in the level of accuracy the rifle is capable of, then add in shooters error and that .7 rapidly becomes a miss. Something to think about.

    That was 0.7 inches drop difference at 350 yards.

    A 1/2 MOA rifle will be shooting a 1.75 inch group.

    You have to be a pretty bad shooter to make that a miss. :D
     

    Speed3

    Ultimate Member
    Aug 19, 2011
    7,816
    MD
    Neck tension was the biggest problem for me and getting numbers and groups to line up. Retired my old brass and began anew. The bullet seating effort was very noticeable between cases. Annealing helped but wasn't a cure.

    So I thought neck tension was always my vertical also....but baffled after a shot yestersay.

    So shooting buddy was getting a sticky bolt, dropped powder charge by .7gr to get rid of that. Still grouped well.

    He is loading using k&m press with force pack (measures force to seat a bullet).

    First 20 pounds were 28-36lbs, the rest were double that pressure. One would assume varying neck tension would drive the seating force, yes?

    His vertical at 600 was the x ring....how does that happen? Doesnt make sense in my brain.

    Dropped a 599-41x! For those that dont know fclass, x ring is 3 inches.
     

    dist1646

    Ultimate Member
    May 1, 2012
    8,758
    Eldersburg
    That was 0.7 inches drop difference at 350 yards.

    A 1/2 MOA rifle will be shooting a 1.75 inch group.

    You have to be a pretty bad shooter to make that a miss. :D

    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.
     

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