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What is 60/40 POI?

Discussion in 'Shooting Related Threads' started by Juantoomany, Dec 20, 2010.

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  1. Juantoomany

    Juantoomany Member

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    I've been shooting for years and maybe I just don't understand...If 50/50 POI is dead flat..What is 60/40 POI?...Before I send a barrel off to be worked on I really want to understand. How do I measure..what do I measure..

    Any help information would be greatly appreciated...As long as I been shooting I feel like an twit for not knowing..

    Dave
     
  2. short shucker

    short shucker TS Member

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    The short version would be the pattern is 60% above and 40% below point of aim.

    ss
     
  3. Juantoomany

    Juantoomany Member

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    Thanks...but the percentages I got...Is there some measurement at a certain distance..and what would that distance be? Center of pattern X number of inches above 50/50 center at X number of yards..this maybe a stupid question sorry...
     
  4. Setterman

    Setterman Well-Known Member

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    You will find it easier to locate your center of pattern above your aim point rather than refer to it as a "percentage".

    EXAMPLE...."My gun shoots the center of it's pattern 4" high at 30 yards" which means when you aim at a target, the center of your pattern is 4" above what you aim at.

    Barrel gurus and stock makers prefer this description over a percentage like "60/40"
     
  5. dverna

    dverna Active Member

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    1-2-many

    Do not waste your money getting any barrel work done. First answer these questions:

    What do you think is "wrong" with your barrel?

    Why is that "wrong"?

    What do you want to achieve?

    Why do you think that will help?

    POI is a personal thing. It depends on the game (trap, skeet, field) you are shooting and how you shoot.

    If you have a gun that shoots well for you, measure the POI above your POA at a given range (note: it is not that important what range you use - just use the same range for all your testing). That will be your criteria and starting point for setting up a new gun. Forget about XX% high or 60/40.

    Don Verna
     
  6. JACK

    JACK Well-Known Member Supporting Vendor

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    Do a search on Neil Winston and recently he had more answers to your query than you will need, but it will help you get what you want fro a bbl guy.
     
  7. Unknown1

    Unknown1 Well-Known Member

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    Samoan Poi and Tahitian Poi are sweet desserts made with coconut milk.

    Hawaiian Poi is like runny stucco but the stucco tastes better.

    MK
     
  8. Juantoomany

    Juantoomany Member

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    Unknown1....It's more like wallpaper paste....you r funny GI...lol
     
  9. mike campbell

    mike campbell Active Member

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    Nothing wrong with the previous advice, re: better to uses "inches high at X yds".

    Here's why it's easier to to get a handle on "inches high" than 60:40, 70:30, 80:20, etc. To calculate the percentages you'd need a calculator and the time to apply some algebra, geometry and trigonometry to find the areas of a circle, a circle segment and a triangle. Those areas are going to be dependent on the diameter of the pattern circle....which is going to vary with the choke and the distance. To get started, you need to pick the distance arbitrarily, but there's no way to predict the pattern diameter for your choke and load until you actually shoot it at that distance. Neil uses 13 yds for his work, stockmakers often use 16 yds, most 16yd trap targets are shot at 30-35 yds ( so 32 would be a good one since it's also 2 x 16) and the standard by which chokes are defined is 40 yds (which happens to be just about 3 x Neil's 13). So, for one reason or another, you'd want to choose one of those yardages and stick with it.

    At 13 or 16 yds, with a Mod, Imod or Full choke your entire pattern will fit on 24" wide paper and it will be fairly easy to find the center (POI) and draw a circle to encompass the whole pattern. If your POI (center) is 2" above your POA (bullseye) at 16 yds, you can expect it to be "4 inches high" at 32 yd...about where the average 16 yd single is broken. If it's 2" high at 13 yds it should be 6" high at 40 yds.

    To answer your question more directly and help compare 60:40 to "inches high", I've done the math and come up with the following:

    1" high @ 13 yds ~ 3" @ 40 yds ~ 63:37, you might say 60:40


    2” high @ 13 yds ~ 6” @ 40 yds ~ 80:20


    3” high @ 13 yds ~ 9” @ 40 yds ~ 95:5

    Maybe somebody can check the math. Hope this helps.
     
  10. Dr A C Jones

    Dr A C Jones Member

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    About a 100 years ago I wrote a programme to demonstrate that percent of shot above the POA was a really dumb method of describing the POI. The problem is the percent of shot varies with the pattern spread even though the centre of the pattern stays constant. You can show this by the above applet - just set a POI above the POA and adjust the pattern spread and see how the percent changes.

    Andrew.
     
  11. mike campbell

    mike campbell Active Member

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    I think the applet is wonderful...thank you very much. I don't, however, see that pattern percentage is a dumb method for communicating POI in layman's (or trapshooter's) terms.

    "The problem is the percent of shot varies with the pattern spread...."


    I'm afraid I don't see that as a problem for what I'm trying to study and communicate.

    If I set the offset at 2.5" (at 40 yd for instance), and vary the pattern spread from 26-40", which I consider a great amount, your applet shows me a percentage of 62-58%, which I consider close enough to 60:40.

    It's a wonderful visual aid, showing the macro picture of the spatial relationship between a clay target and the pellet swarm. I see no value in distinguishing between a 26" pattern that is 62:38 and one that is 40" wide and 58:32. Shooting 10" high I'd get 90:10 and 80:20...which for my practical purposes are no different.

    I know that 470nm wavelength light is "blue" and 490nm is "bluegreen." That might be useful for making dyes, but it wouldn't communicate much to the salesperson when I'm shopping for a shirt. Thanks again for the wonderful tool.
     
  12. Neil Winston

    Neil Winston Well-Known Member

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    Mike it is a dumb method for communicating POI in anyone's terms. It has several drawbacks.

    1. It add nothing to the information that the gun shoots NN inches high at nn yards. Once you know that - and if you are talking about where a guns shoots you have to know that or you don't know where it shoots - why translate it into a secret code that only the guys and gals "in the know" can understand?

    In fact, I think that blocking communication is its purpose for many people. Say I bought a gun on this site which was said to shoot "70/30" and it shoots some distance from that. The seller might well claim that "70/30" is so ill-defined and misunderstood that the fact that this one does not do that is no reason for me to get my money back.

    2. It is, as commonly defined, intellectually indefensible and anyone who thinks is going to be offended by people who claim to be able to "explain" it and then simply run off what is clearly total BS, stuff that a twelve-year-old would not try to get away with in a grade-school classroom.

    There are, Mike, how many definitions of "percent high?" I think I can cover three and the problems with each without even referring to notes.

    Definition A. "Percent high is the percentage of the pellets in a load which travels above the point of aim of the shotgun."

    This definition at least has the virtue of truthfulness and if anyone were to actually use it, he would at least have a number he could defend, but I'm not sure what he should do with it. It would require, after all, that he actually count the pellets above and below the POA. Do you know anyone (besides me in testing this theory) that has actually counted the pellets in a pattern to get this information? And what did he then do with it? That is, what is the utility of such knowledge, especially in light of the effort it takes to get it?

    Definition B ""Percent high is the percentage of the pattern in a load which is above the point of aim of the shotgun."

    Notice the subtle change from Definition A. "Percentage of pellets" has changed to "percentage of pattern."

    This is the way people who don't count pellets (and, if my guess is right, don't test where their guns shoot) like to talk. There is, after all, no way to guess what they are talking about. What is a percentage of a pattern?

    What happens is they make up "patterns" which contribute to these mythical "percentages" which are so unlike real patterns they might as well be talking about something else entirely.

    Kay Ohye, Stan Baker, and, following their lead, almost everyone else, I fear, promotes the idea that ten percent of a pattern is three inches. That is, a 50/50 pattern is right where you point the gun. Since the pattern is a 30-inch circle, there is 15 inches of it above, 15 inches below the point of aim. So take that 15 inches, divide it be 5 (the number of 10% steps to 15 inches high,) and you conclude that every 10% high is equivalent to 3 inches.

    Which is fine except that it is not faintly true. It would be true if patterns were

    1. evenly distributed and

    2. rectangular.

    But they are neither. They are, in a general sense, round not square, and more concentrated in the center, not evenly distributed, even if the choke is made out of titanium.

    My question is why would anyone want to use a system that makes no sense? Especially in contrast to one which is so clear, so true, and so universally understood, the system of simple measurement in inches.

    Definition C. A retreat from Definition B in that patterns are admitted to be round and hot in the center. This is what you see on Andrew Jones' linked program. No one has ever claimed that there is a simple distance high/percent high relationship here but if percent high really did equate to "percentage of the pattern in a load which is above the point of aim of the shotgun" this is where you would find it.

    My personal feeling is, MIke, that the only people who say "My gun shoots 70/30" have no idea where their gun shoots at all because they have never tested it. In other words, it's just pure BS.

    In contrast, I think that people who say "My gun shoot 5 inches high at 40 yards" are likely to have made an effort to find out and their subsequent opinions on the subject of POI are worth listening to.

    Neil
     
  13. mike campbell

    mike campbell Active Member

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    Neil,

    "2. It is, as commonly defined, intellectually indefensible ..."

    I define it one way, this way....

    "Definition A. "Percent high is the percentage of the pellets in a load which travels above the point of aim of the shotgun."

    "This definition at least has the virtue of truthfulness..."

    I agree. Not only is it intellectually defensible, it is meathematically "truthful" and graphically demonstrable.

    "and if anyone were to actually use it,"

    I do.

    "he would at least have a number he could defend, but I'm not sure what he should do with it. It would require, after all, that he actually count the pellets above and below the POA. Do you know anyone (besides me in testing this theory) that has actually counted the pellets in a pattern to get this information? And what did he then do with it? That is, what is the utility of such knowledge, especially in light of the effort it takes to get it?"

    Depends on how you choose to define the "number." I thought I made it clear in my earlier post that I won't (don't care to, don't need to, I don't plan to write a computer program, an article for a magazine or a pHD thesis) try to distinguish between 75% high and 80% high. For 60-70, 80-90 and 100+% high...the ONLY pecentages I care to quantify, I don't need to count pellets. I assure you, but don't give a Rat's a$$ whether you believe it, that I can shoot 3 shells on one pattern and estimate those within the margin of error that concerns me with only a pencil and a string and an eyeball. How many patterns do you have to shoot to unequivocally state a gun shoots 2" high and not 3" high, which is you preferred measurement?

    "My question is why would anyone want to use a system that makes no sense? Especially in contrast to one which is so clear, so true, and so universally understood, the system of simple measurement in inches."

    It makes sense to me and is actually useful for quantifyng how high a shotgun gun shoots. In contrast, inches high is meaningless to me UNTIL I TRANSLATE IT TO A MENTAL IMAGE of a circular pattern of a given size at certain yardage. Let me say that again...I find it PRACTICAL. For shooting that is, I don't sell trap guns.

    An inch measurement is a point measurement....makes perfect sense to me to know that a rifle shoots 3" high at 200yds. With a gun that groups 5 .224" projectiles in a 1" circle at 200 yds, I know just where to put the crosshairs to put one of those projectiles in a prairie dog's head if he's at 175-225 yds. If, in fact, it shot 5" high and I didn't know it, I'd likely miss.

    I don't necessarily break a rising clay target with a pellet anywhere near a point 6" above my point of aim. Bt I believe I'm likely to break it with one of the 80% of the pellets in my shell that are somewhere above the plane, and possibly left or right of my POA.

    Neil wrote..."I doubt many are satisfied with my descriptions of vertical POI
    placement so far. “Flat,” “just a little high,” and “high” are hardly
    what you expected be able to tell the guys at the club."

    Works very well for me, Neil. I'd say "flat" is 50-60% high, "moderately high" is 70-80% and very high is 90+%. WTF does 3 inches mean?

    That's a rhetorical question. I find the tone of your comments directed at me insulting. I won't be continuing the exchange. You and Andrew can preach to each other and I promise not to interrupt. I do hope you eventually agree on which one of the 400 pellets that interests you is likely to be 3 inches high.
     
  14. Neil Winston

    Neil Winston Well-Known Member

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    I'm not at all sure what you are getting at, Mike. After what I wrote, I somehow expected a similar-length defense of the "percent high" concept from one of its advocates, which it seemed to me you identified yourself as.

    I anticipated that you might describe how the figure is arrived at by its users, some pointers for novices on getting it right, and a list of reasons why it is better and communicates more or more-useful information than a bare statement of distance from POA at what distance the test was made. For example, three inches high at thirty yards.

    Instead, all I do is read my own post again. Followed by the inscrutable

    "I do hope you eventually agree on which one of the 400 pellets is likely to be 5 inches high."

    I admit it, Mike. I don't get that at all.

    In the spirit of cooperation, I'll even begin a post for you.

    "If you want to determine the point-of-impact of your gun using percent-high notation . . ."

    Well, you can take it from there.

    Neil
     
  15. Neil Winston

    Neil Winston Well-Known Member

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    Since the post I was responding to has changed so much since I responded to it, I'll give the new one some time and thought.

    Later edit. I read that Mike will have nothing more to say on the subject and I guess I'm content with the reservations I expressed about percent-high as well. I'll respond if asked, or course, but otherwise I'll just let it stand as written.

    Neil
     
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