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Testing point of impact at 13 yards (Winston)

Discussion in 'Shooting Related Threads' started by Neil Winston, Dec 4, 2008.

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  1. Neil Winston

    Neil Winston Well-Known Member

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    Here's a old thread, reposted.

    There are a couple of threads active about POI, adjustable ribs, and so on. Here are some ways to find out up close that vital question "Where does this thing shoot?"

    I recommend 13 yards because, as you'll see, I can make some guesses about patterns at that distance as well. I also think that a bench rest of some sort is necessary, as just taking one shot at each "target" so you can keep track of what's going on and how you are doing. Paper, a wide magic marker, and no wind and you're in business. Bring a notebook as well; you will do a lot of this in your trapshooting career and you might as well start keeping records now.

    1. (After checking what's beyond your paper target to make sure it's safe - you won't be able see while you are shooting.) Draw what looks like a tic-tac-toe grid on the paper with the intersections about a foot apart.

    2. Mount your gun as usual and look at your "sight picture", that is how you see the barrel, rib, beads, and all that. Do it a few times so you can remember.

    3. With your bench rest (table, auto hood, stack of shell flats - you get the idea) at a place where it puts your muzzle about 13 yards from the paper, sit down (I think that's important too), and put the gun up so you see down it in the same way you did when you were trying to get that right earlier.

    4. Use light 7 1/2 name-brand shells or your own good reloads of the same type. Putting the front bead _just at_ the base of one of the crosses at the paper make a shot. If you've been shooting long you jerked the gun as you shot and so you threw that shot away. So do it again, at another cross, and this time try to make a better, smoother trigger pull.

    5. If you are using a full choke you see two holes in the paper, one from the shot and the other from the wad. As testing continues, you'll see that the wad hole is upper-right now, then lower-left, then dead-center and so on and will then believe, correctly, that where the wad goes has nothing to do with where the shot goes so you can't use the wad to tell where you are shooting.

    6.After a few shots, each at a different cross, you'll have some holes (or little patterns) with a fairly consistent relationship to the crosses they were associated with. What to make of them? Well here are some and here's what they mean.


    We'll start with a Perazzi O/U Ithaca-era, top full and bottom less so.

    [​IMG]

    Individually they look like this, starting with the top one:

    [​IMG]

    This is what a full choke does; it just drills a hole with some pellets around it as well. You can't split hairs here, so this barrels shoots flat. (calculations to follow)

    Again, here's that O/U pair a little closer:

    [​IMG]

    And we'll zoom in on that bottom one:

    [​IMG]

    Now two things are apparent. First the pattern is lower in relation to the cross than was the one from the upper barrel. It started lower, so that can account for about an inch of it, but still, it _is_ lower anyway. Second it's not that nice round hole from the full choke, but rather it's sort of "lacy" and if you pushed the paper back it, a lot of it would still be there. This is typical of an improved modified choke with 7 1/2's at this distance, and that's just what this unmodified Perazzi has. Should we conclude that this barrel shoot low because we made this shot? Not, yet. Look back at that first picture again:

    [​IMG]

    On that one, the right-hand pair has the lower barrel shooting a lot closer to the cross, close enough that, considering where it started from, you can estimate that it shoots just like (but more open than) the upper one. You see, you can't go by any one shot, or, I think, even one day of testing. You have to do this a bunch of shots, and at least a couple of days, before you are satisfied (or ready to panic, whichever the case may be).

    That about covers the flat-shooters; here's a high one, my Bowen when I built the comb up to try it. It didn't work and I'm back down, but that doesn't say it won't work for you.

    [​IMG]

    Set up like this the Bowen shot eight or ten or more inches high at 40 yards. Yours will too.

    Let's close with a couple of more-average shooters. It's a Baker backbore and choke set for an MX-8 again. The top is 0.040 choke, the bottom is marked "16 yards." I've posted them together you can get an idea of the scale.

    [​IMG]

    Here’s the upper, the full choke, a blasted-away hole:

    [​IMG]

    The half-inch deviation to the side doesn't mean a thing; if it was twice that and over and over again, I'd begin to worry,but only begin to "take note" pending further testing tomorrow.

    And here's the 16-yard choke:

    [​IMG]

    It's way more open, isn't it? No holes, just a nice round pattern. This is how a modified choke shoots light 7 1/2's at 13 yards.

    How about where that Baker barrel shoots? It's about 2 inches high, I'd call it somewhat high, maybe 5 or 6 inches high at 40 yards.

    I'm going to take a break and take Kyra up to Metro for me to socialize and her to run. I'll fill this in with the rise vs. fall calculations when I get back.

    Yours in Sport,

    Neil
     
  2. Shooting Coach

    Shooting Coach Well-Known Member

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    Thanks for the re post. Neil, I have shamelessly stolen your technique, but I do call it the "Winston Method". This is the common sense and highly effective way to make this chore short, sweet, and sure.

    I have seen some really ineffective and plain laughable ways to do this performed by supposedly knowledgeable trainers.
     
  3. shot410ga

    shot410ga Well-Known Member

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    Thanks for the repost. I've used your method, and it seems to work great.
     
  4. shootsome

    shootsome Member

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    Thanks for the re-post Neil. I appreciate the help.
     
  5. Jon Reitz

    Jon Reitz Well-Known Member

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    This is not how Kolar does it.
     
  6. 870

    870 Well-Known Member

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    Sportshot:

    The upper full looks "lacy" to you? Seems pretty tight to me.
     
  7. mirage1

    mirage1 Member

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    Thanks for the post Neil.So if a pattern shoots 2 inches high at 13 yards
    is it safe to assume it shoot 6 inches high at 40 yards?
     
  8. miketmx

    miketmx Well-Known Member

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    I bought the TMX used about 22 years ago and patterned for POI several times and verified the results with the Neil Winston 13 yard method which is much easier to find the center of the pattern. I am still amazed by the number of posters to trapshooters.com who seem to prefer a 100% or 15" over the bullseye at 40 yards POI. My gun shoots about 8 or 9 inches high at 40 yards and when ever I raise the comb my scores go in the tank until I bring the sight picture back to normal. I don't have to daylight a target or blot it out but how do you guys shoot a gun with a 100% high POI ??
     
  9. white rattler

    white rattler Member

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    Mike, You and I have had this talk many times in the past. I shoot a 100% high gun and if I can hold the gun and not move anything until the bird clears the rib and then make a nice smooth move over to the bird it will break the target. I am looking at the leading edge of the target and all I can tell you is that the gun comes up to the spot on the target that I am looking at and I pull the trigger. Trevor Dawe. PS Merry Xmas to you and Trudy.
     
  10. miketmx

    miketmx Well-Known Member

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    Thanks Trevor and Merry Christmas to you and Ursula. There have been many threads that say it doesn't matter how much rib you see when you get the right POI. For my fixed rib gun it does seem unnatural to have a lot of space between the beads and I end up with more cheek pressure on the comb than is comfortable. Maybe that is why they make adjustable ribs.
     
  11. phirel

    phirel TS Member

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    mirage1 - A gun that shoots 2 inches high at 13 yards will not shoot 6 inches high at 40 yards because of gravity. Between 13 and 40 yards, the shot will fall about 2.5 inches and will rise above the POA three times the distance from the front sight to the center of the bore. Two inches high at 13 yards typically works out to around 5 inches high at 40 yards and using the old method, could be described as a 70/30 pattern.

    MY PERSONAL OPINION- At 13 yards make sure your gun is not shooting to the right or left. This can be very difficult to determine if you pattern at a distance greater than 13 yards. It is not easy to transfer how you shoot the gun from a rest to how you shoot the gun on the line. I always recommend adjusting the gun to around 2.5 to 3 inches high at 13 yards and then shoot a few thousand registered handicap targets. After that, make any additional adjustments that you believe might help.

    Pat Ireland
     
  12. phirel

    phirel TS Member

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    The goal is to determine the point of impact at 40 yards. When looking at a 40 yard pattern, it is difficult, perhaps impossible, to accurately identify the center of the pattern. It is easy to identify the center of the pattern at 13 yards and 13 X 3 = 40 (almost).

    Pat Ireland
     
  13. chuckles

    chuckles Member

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    13yd works for me to tell hi, lo, left, right, but want to add that it is very important(at least for me) to know what a specific choke pattern looks like at 40 yds re density, holes, POI....Mod vs Imp Mod vs Full....

    I usually do both...

    regards
     
  14. phirel

    phirel TS Member

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    chuckles- I agree with you. POI at 13 yards, pattern analysis at 40 yards. They are two different unrelated things.

    Pat Ireland
     
  15. Garry

    Garry Active Member

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    For Neil and or Pat,

    Please complete the following chart.

    Inches high or low at 13yds. Equals X inches at 40yds. %above/below
    +4
    +3
    +2 5 70/30
    +1
    0
    -1
    -2
    -3
    -4

    Thank you
     
  16. Garry

    Garry Active Member

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    I don't know how to delete my first post so I will try again.

    A gun that shoots 4 inches high at 13 yards will shoot ? inches high at 40 yards and the percent above and below would be ?

    A gun that shoots 3 inches high at 13 yards will shoot ? inches high at 40 yards and the percent above and below would be ?

    A gun that shoots 2 inches high at 13 yards will shoot 5 inches high at 40 yards and the percent above and below would be 70/30.

    A gun that shoots 1 inch high at 13 yards will shoot ? inches high at 40 yards and the percent above and below would be ?

    A gun that shoots 0 inches high and low at 13 yards will shoot ? inches high at 40 yards and the percent above and below would be ?

    A gun that shoots 1 inch low at 13 yards will shoot ? inches low at 40 yards and the above and below percent would be ?

    A gun that shoot 2 inches low at 13 yards will shoot ? inches low at 40 yards and the percent above and below would be ?
     
  17. zzt

    zzt Well-Known Member

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    Garry, the old "percentage" system was based on an idealized 30" diameter pattern at 40 yards. If the pattern was centered on the POA it was said to be a 50/50 pattern, because half of the pattern was above and below the POI. If the POI was 15" high it was said to be a 100/0 shooter, because all of the 30" pattern was above POI. In between, it was just divided up with 3" equaling 10%. So 3" high at 40 = 60/40, 6" high = 70/30, 9" high = 80/20 and 12" high equals 90/10.

    The answer to your other question depends on what degree of accuracy you want, and what the rib height of your barrel is. There is no universally accurate formula for extrapolating POI at 13 yards to any distance other than 26 yards. If you shoot a top single, or a flat ribbed O/U or equivalent like an MX-15 or a K-80 you can simply take your POI at 13 yards, multiply by 3 and get an answer accurate to within about an inch.

    I test POI on my trap guns (tight chokes) at 20 yards. I have zero problems determining the center of the pattern at that distance and extrapolating is easy. Just double the measurement to get POI at 40. The most accurate way to set your POI, or find out what it is in the first place, is to shoot a 1/2 the distance you are interested in. Say you're interested in your POI at singles distances, 34 yards. Shoot for POI at 17 yards and double the result.

    Shooting for POI at half the target distance you care about is the most accurate way, because any bore/bead distance is automatically accounted for accurately. In other words, it just doesn't matter what gun you are shooting. If you shoot at shorter distances and try to extrapolate to 2.5x or 3x distances, error creep in. The higher your rib in relation to your barrel, the bigger the error. That's why I suggest shooting for POI at 1/2 the distance you are interested in and doubling it.
     
  18. Frank C

    Frank C Well-Known Member

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    I have never tried the 13 yd technique, but will at some point....what I have done is take a LARGE sheet of paper, draw a 30 inch circle, then fold it in quarters, now you will have 4 quadrants. draw your "bird" in the middle, go out to 30 yds and shoot at it. of course you will have the slight wavering of the "point" so you will have to repeat several times on different papers. what you will have is most of the pellets in the circle. Then with a highlighter I count the pellet hits in each quadrant and calculate the ratio 60/40 etc. works for me YRMV....FC
     
  19. crusha

    crusha TS Member

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    Why 13 yards? Why not 12?


    Is this another case of the Roman Chariot wheels being based on some dimension at the Minneapolis Gun Club?


    Just curious.
     
  20. Neil Winston

    Neil Winston Well-Known Member

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    Dear J. Curious,

    The dimension you ask about is _not_ at the Minneapolis Gun Club at all. It is rather the distance between the pattern board and the line formed by the rear of the traphouses at the Metro Gun Club, almost 50 miles away from the MGC. It was an easy way for me to place the benchrest at a repeatable distance without tedious measurement and the rest of the advantages - the ease of distance conversion and the ability to roughly gauge patterns - they just happened by on chariots, as you guessed.

    Ben H
     
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