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center of pattern

Discussion in 'Shooting Related Threads' started by Traders, Jun 19, 2012.

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  1. Traders

    Traders Well-Known Member

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    I know this has been discussed before, but I still haven't got it straight in my pea brain.

    How do you calculate the center of the pattern above the aim point. In other words if the center of the pattern is, for example 2 inches above the aim point at 13 yards, what is it a 30 yards, etc.

    Thanks
     
  2. Stl Flyn

    Stl Flyn Well-Known Member

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    Why not test the gun at thirt yards. Then you know for sure what the pattern is doing. Understand also that this method determines the point of aim distance, not point of impact. They can be very different because of the fact that you are not aiming a shotgun, when shooting at a moving target..

    Put the target out at thirty yards, and use an upright post to hold your gun steady in your normal shooting position. Put the bead on a black mark on the paper toward the bottom quarter of the paper, and squeeze the trigger. Measure the distance between the patterns outermost pellets and figure out the center. Make a mark on the paper at the halfway distance. Where the marks intersect is the center. Draw a circle around the outermost pellets, using a string and pencil, anchoring the string at the center of the pattern. Measure from the center of the circle to the target, and there you have the point of aim difference. Exclude some of the flyers. You can pretty much tell which ones are the flyers. This is what it would look like in the photo. This one was 8 1/4 inches high at forty yards.
    stlflyn_2010_0704232.jpg
     
  3. atra_service

    atra_service TS Member

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    Are you testing at 30 yards or 40 yards?? I was always told 40 yards with a 30" circle.
     
  4. Tech Writer Jeff

    Tech Writer Jeff Active Member

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    Stl Flyn: why is it necessary to draw the circle at all? All you're interested in is the difference between the pattern's center POINT and the aim point, which you already found.

    atra_service: A 30" circle at 40 yards is the agreed-upon standard for evaluating choke performance . . . it has nothing to do with POI.
     
  5. Ed Y

    Ed Y TS Supporters TS Supporters

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    Not too many ATA targets shot at 40 yards. I like to pattern trap loads at 32 yards.

    Ed Yanchok
     
  6. atra_service

    atra_service TS Member

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    Well I'm glad you cleared that up for me, here I've been testing for POI at 40. Didn't mean to hi-jack this thread!
     
  7. Garry

    Garry Active Member

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    "if the center of the pattern is, for example 2 inches above the aim point at 13 yards, what is it a 30 yards?"

    The POI would be 4.6 inches high at 30 yards.

    The POI would be 6.1 inches high at 40 yards.
     
  8. senior smoke

    senior smoke Well-Known Member

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    Years ago, I asked Vic Reinders how do you pattern a gun to see where it shoots? He pulled a soda can out of the garbage and placed it on the ground 10 yards in front of him.

    He shot at the can and hit it dead on. He said now try your gun. My pattern went over the can and made a mark in the grass. he said your gun shoots high. Vic said if your gun shoots low the mark in the grass will be in front of the can.

    I then asked Vic about percentages? He laughed and said I just showed you on my gun that I need to touch the bottom of the target to break it. With your gun, you need to see a shade of daylight.

    He said you do not need to know any more than that to break targets. He said the name of the game is breaking targets, not percentages. Vic always felt shooters make this game harder than it actually is.
    Steve Balistreri, (enough said)
     
  9. Tech Writer Jeff

    Tech Writer Jeff Active Member

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    atra_service said: "Well I'm glad you cleared that up for me, here I've been testing for POI at 40 yards".

    You can test POI at any distance . . . whatever distance that interests you, including 40 yards if that's what you want to do. But the 30-inch "patterning circle" is irrelevant for this. Point of Impact is exactly that . . . a POINT . . . not a pattern. Pattern attributes (overall pattern size, pellet density) are controlled by factors such as choke performance and ammunition quality. These are evaluated independently from POI.
     
  10. Unknown1

    Unknown1 Well-Known Member

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    You're wasting heartbeats trying to find the center of your patternS. That changes with each shot; sometimes a little and sometimes a lot.

    Use Neil Winston's method for finding the POI of a barrel/choke/bead combination..<UL><LI>put your target 13 yards away with an aim point clearly marked in the center of a large cross (1 each, bold vertical and horizontal line) drawn on the target<LI>install your tight choke<li>from a steady rest, fire your regular trap load aiming directly at the aim point</UL>The shot will make a distinct 1/2"+ hole marking the point of impact achieved (vertically and horizontally) by firing at the aim point. Multiple the vertical and horizontal deviations from point of aim by 3 to get the approximate deviation at the target break distance.

    Keller
     
  11. DTrykow

    DTrykow Active Member

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    40Yards is the standard. Neil's is also: 13yd X 3 = 39yds aka 40yds. IMO At 40 yards you get more data. POI out where you break the target, Choke performance: How the choke is patterning, if there are any holes in the pattern or is it Left, right. I use Neil's 13yd to see if the gun is shooting straight so I can move my comb to adjust and chokes also will/can skew the pattern left or right. Choke for smoke. Dave T.
     
  12. Stl Flyn

    Stl Flyn Well-Known Member

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    TWJ,

    I included the circle for pattern reference. Gives you a better idea of what is happening.

    This was a Browning BT-99 Competition. 1 1/8 oz. of 8's, 1235 fps., at forty yards. I do not recall the letters in the serial number, but remember it to be a early eighties gun. I must say it was a very consistent pattern. No holes in the pattern of a 28 1/2" circle.

    Steve,

    I could not agree more about us making this game much more involved than necessary. If you look at how Vic shot, and approached the game, with the gun he had, standard fixed choke Model 31, it is no wonder how today we should not miss, with all of the new technology, calculations, and alterations to the barrel and stocks. Just really does show you that if the gun goes bang, it is not the gun that is to blame for the missed target. Jon
     
  13. Johnny

    Johnny Well-Known Member

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    Ed Y , Lots of people pattern at 30 some yards, but to me it's like the guys shooting at a pop can or target box in front of the trap. It doesn't tell me anything unless I can relate it to 40yds.
     
  14. Tech Writer Jeff

    Tech Writer Jeff Active Member

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    Stl_flyn said: "I included the circle for pattern reference. Gives you a better idea of what is happening".

    Exactly my point why the circle is not necessary to answer the Original Poster's question (which concerned POI only). POI and pattern quality are completely different things. Whenever a shooter starts analyzing both at the same time, they often start changing POI because pattern size/quality tricked them into thinking there was something wrong with their POI.
     
  15. senior smoke

    senior smoke Well-Known Member

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    Jon:
    Vic Reinders told me that most shooters miss targets from the neck up. He said once you know where the gun shoots any misses are on you, nothing else.
    Steve
     
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