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MOA Question

Discussion in 'Rifle Country' started by jon8777, Apr 11, 2010.

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  1. jon8777

    jon8777 Member

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    Shot the 223 tonight at 100, 150 and 200 to verify the balistics on my mil-dot chart. I shot 3 shot groups 10 minutes apart with a 3-5 mph wind at my back.

    I came home and started looking at the numbers and I need a second opinion to verify my math.

    Heres my results for the groups shot from bipods with a rear bag prone on the ground.

    100 yards 0.552"
    150 yards 0.617"
    200 yards 0.733"

    In theory I should have shot a 1.104" group at 200 yards, but its grouping smaller as I shoot further. (Typically this gun shoots in the .7-.8" at 200 yards.)

    What is the proper way to determine the MOA of this load? Use the 100 yard group as MOA or divide the group size into the yardage and average the 3 distances?
     
  2. Zak Smith

    Zak Smith Moderator Emeritus

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    If the sight picture was different, or your shooting position was different at the different ranges, that can account for different levels of accuracy.

    If you are consistently shooting 0.7-0.8" at 200 yards, it might be worthwhile to figure out why your leaving accuracy on the table at 100.
     
  3. jon8777

    jon8777 Member

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    I shot the same position and hold.


    The scopes a 3200 10x fixed MD
     
  4. hadmanysons

    hadmanysons Member

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    Bullets do not fly in a "straight" line all the way down the range. People tend to think of it as a funnel, the further out you get but that is not always true. I wish i had the link to the video explaining it because its hard to describe. Assuming that you an excellent marksmen and everything is staying super consistant between the different ranges, there may be nothing wrong with the group size. The bullets just might be corkscrewing as they get further down range.

    Now, this is a new concept to me and i'm not sure i believe it yet either but it is something i have heard of and seen. I might be talking out of my @$$ but this could be what's going on.

    Does anyone else remember what i'm talking about?
     
    Last edited: Apr 12, 2010
  5. bhk

    bhk Member

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    I am not too sure you are using the term MOA accurately, making answering your question a little difficult. MOA stands for 'minute of angle,' and is about 1.05" at one-hundred yards. That would be 2.10 at two hundred, 3.15 at three hundred, etc. Most folks just round this off to 1, 2, and 3 inches.

    I think you are really talking about group size. A MOA group at 100 yards (one inch group) has always been an accuracy goal for shooters. Your rifle is shooting considerably under MOA at the ranges you are listing. That is one wonderfully accurate rifle. As far as the groups tighting (in respect to moa) at longer ranges, this is not unheard off and relates to the fact that some bullets take considerable flight time to properly stabilize.
     
  6. wishin

    wishin Member

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    I would express your accuracy as follows:

    100yds - .55" MOA

    150yds - .93" MOA

    200yds - 1.47" MOA

    All are sub-MOA. To average them out would be mixing apples and oranges IMO. I could be wrong, but that's how I would tell someone what MOA that particular gun shoots.
     
  7. Zak Smith

    Zak Smith Moderator Emeritus

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    This is all wrong, and using units of " MOA (literally inches MOA) also doesn't make any sense.

    0.552" at 100 yards is 0.552/1.0472 = 0.527 MOA
    0.617" at 150 yards is 0.617/(1.0472*1.5) = 0.393 MOA
    0.733" at 200 yards is 0.773/(1.0472*2) = 0.369 MOA
     
  8. bhk

    bhk Member

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    WRONG!!

    He is shooting:

    .53 MOA at 100 yards (MOA at 100 is 1.05 in.)

    .39 MOA at 150 yards (MOA at 150 is 1.58 in.)

    .35 MOA at 200 yards (MOA at 200 is 2.10 in.)

    Edited: OPPS! ZAC BEAT ME TO THE CORRECTION. Actually Zac's answer is more correct than mine because he is rounding off MOA to four places and I rounded off to two places.

    .
     
  9. jnyork

    jnyork Member

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    If I had a rifle that shot like that I dont think I would be worried about such minor things as this. :)
     
  10. NMGonzo

    NMGonzo Member

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    if I can hit a card from a deck taped to the target at a 100 yards I am as happy as I can be.
     
  11. 3:00hold

    3:00hold Member

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    Shoot 20 3 shot groups at each range and tell me the average. If 200 yards isn't 2x 100 yards (or greater) then you are going something different or you have a psycological issue with shooting at 100 yards.

    Comparing two three shot groups is statistically meaningless.

    Loosely, MOA is 1" at 100 yards, 2" at 200 yards, etc.
     
  12. jon8777

    jon8777 Member

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    As soon as I posted I realized my use of 'MOA' was incorrect.

    I am not complaining about the accuracy of the gun. I am very happy with it after last summers looooonnnnggg load testing, gun tuning and final scope selection. Now I need to start verifying my MD guestimates to actuall ground hog 'target' results. I have two ( 2/2 ) field target results with the MD scope so far this year. I am still getting use to using the MD for hold points, its nice but its taking time to get use to.

    I was looking for why or what is causing my groups to measure a smaller MOA calculated group sizing as the target is further out.

    I am not seeing any signs of keyholes/oblong holes in the target up to 200 yards (rifle ranges max distance) and I have fired 200+ rounds thru this gun working on the load.

    When you talk about the funneling of the bullet, my guess is the group will eventually reach a point where the group begins to grow in respect to MOA?
     
  13. jmr40

    jmr40 Member

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    There have been several discussions about this here and at other forums recently. No one has come up with concrete proof to either prove or disprove the theory but a lot of people believe that under the right conditions bullets become more stable after a short distance after being fired. This results in better accuracy than expected at longer ranges. Others theorize that shooters just concentrate better because the target appears smaller at longer ranges.

    I've experienced the same thing many times. I believe there is something to the bullet becoming more stable after a point in it's flight, but cannot offer any real proof.

    I will only say that with some of my rifles I quite often get groups similar to yours. Some of my rifles shoot the same MOA pretty consistently at all ranges, just as one would expect. Other rifles I own very often shoot as yours did, getting slightly better MOA as the range increases. If I were just concentrating better at the long ranges I would see the same with all of my rifles.
     
  14. MCMXI

    MCMXI Member

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    It may be your sight picture as Zak mentioned. You have a fixed 10X scope so it's quite possible that your brain/eyes/muscles prefer the percieved reduction in reticle movement on the target at 200 yards. That's my best guess since shooting is 90% mental (so they say). If you had a variable scope such as a 3-9x, you could try 3x at 100 yards, 6x at 200 yards and 9x at 300 yards. Now that would be interesting.

    :)
     
  15. Ridgerunner665

    Ridgerunner665 Member

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    In reference to Zak's first post...

    Parallax? Makes sense...the scope is probably preset at 150 or 200 yards.
     
    Last edited: Apr 13, 2010
  16. M1key

    M1key Member

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    Sub 3/4 inch groups at 200yds with an AR? That's almost competitive in bench rest...

    The term is "going to sleep". Seems the boattails rotational pitch slows and stops "wobbling" anywhere around 150 yards. The 200 yard groups are often tighter (MOA-wise) than 100 yard groups. Match shooters have known this for years...

    I have noticed it mostly shooting heavier (read longer) 308 match boat-tails from a bolt gun. Groups can run .50 to .75 inches @100 yards and still group .75 inches or less at 200.
     
  17. MCMXI

    MCMXI Member

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    I still don't believe this "going to sleep" theory. I'm certainly not saying that it's not true, it's just that I've NEVER worked up a load that was more accurate at 200, 300, 600 or 800 yards compared to 100 yards.

    Did the OP state that he was shooting an AR? Maybe I missed it.

    :)
     
  18. fractal7

    fractal7 Member

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    Type of Target

    I just kind of stumbled on this thread and find it pretty interesting. What kind of target are you shooting at? Shape, color etc... If the aiming point gets smaller perhaps its easier to aim at the point rather than the "middle" of say a larger black circle at 100 yards. May not be the answer but just another theory to throw into the mix.
     
  19. jon8777

    jon8777 Member

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    The first scope that was on the rilfe was a 3-9x40 and with variable power settings the groups were the same.

    Nope, not an AR... Like to have one but I'd have a mint into one... not that its a bad thing.

    So the 'going to sleep' is gun to gun or is it based on the bullet?
     
  20. M1key

    M1key Member

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    Sorry, my mind was on "AR" at that moment.

    Whatever the phenomenon referred to as "going to sleep" is, it is fact. I have heard this from match shooters using boattails and I have done it myself on a number of occasions...at least to 200 yards.

    I understand VLD bullets (very low drag) with protracted boattails were developed (in part) to minimize this effect. Has something to do with ballistic coeffiecient of friction...but I slept through that part of the class.

    Lapua 170 match have a bit of a rebated boattail.
     
    Last edited: Apr 13, 2010
  21. jon8777

    jon8777 Member

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    B/W grid compliments of the Oce plotter from work.

    I have tried combinations of black, yellow and red home grown targets over the years and never noticed a difference in groups. Some people see different colors better.
     
  22. jon8777

    jon8777 Member

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    Np


    Your talking the Barnes VLD bullets?
     
  23. M1key

    M1key Member

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    I was thinking Berger...I have a few boxes of their 308 match VLD and they have a very LONG BT and a long OAL...too long for a lot of mag-fed rifles.
     
  24. jon8777

    jon8777 Member

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    Wrong 'B'...

    Yes the longer heavier bullets shoot better than the shorter bullets of the same weight.

    Length of bullet is not a problem, just not sure if I want to start down the road of working up a new load.
     
  25. ArthurDent

    ArthurDent Member

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    Could it just be random variability in group size?

    3:00hold,

    You now have my interest and respect.

    I had been reading this thread with some interest and curiosity as I have been working hard to improve my accuracy. The more I study this problem, the harder it gets. This is fun and frustrating!. :)

    I had been reading this thread, wondering if there was some new phenomenon of external ballistics I didn't yet know about. I had forgotten the key point of statistics, and you reminded me of it, 3:00hold. Your procedure of averaging groups is exactly correct! :)

    I have started [thread="517405"]a thread, here,[/thread] on some math I've played with on this subject.

    The bottom line results for this particular situation are: For a 3-shot group, you can expect the center-to-center measurement (ctc) to vary over a quite wide range. For instance, if your average ctc measurement for a 3-shot group was 1.0 MOA, you would expect a particular ctc measurement to vary between 0.44 and 1.65, 90% of the time. That is a huge range!

    Sooo, jon8777, it is quite easy to believe that your single measurements of 3-shot groups could vary between 0.53 and 0.37 MOA. I would be interested in seeing the results of the averaged measurements as described by 3:00hold.

    In any case, I'm still quite jealous. My groups are nowhere near that tight yet.

    ArthurDent.
     
    Last edited: Apr 14, 2010
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