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Testing POI and pattern close - photos (Winston)

Discussion in 'Shooting Related Threads' started by Neil Winston, Mar 31, 2010.

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  1. Neil Winston

    Neil Winston Well-Known Member

    Joined:
    Jan 29, 1998
    Messages:
    7,848

    Here's an 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. crusha

    crusha TS Member

    Joined:
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    5,762
    In order to make any real conclusions, don't you need to repeat the test with _white_ paper?


    All you've done is prove where your gun shoots on brown paper.
     
  3. phirel

    phirel TS Member

    Joined:
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    Messages:
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    Neil- I do agree that several (ca 10) shots are required to get a true measure of the POI. I do not understand your thought that testing over different days is good. Are you considering shooter error, wind, humidity etc. We both know that high humidity would result in the gun shooting higher, but the difference would be so slight that it could not be measured. (High humidity = reduced air resistance = greater velocity = less time for gravity to pull the shot down). I would guess this factor would raise the POI around 1/1000 of an inch. This might make a nice esoteric discussion.

    Pat Ireland
     
  4. Uncle Sam

    Uncle Sam Member

    Joined:
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    I wanna meet Kyra some day....I hope to have some doggie treats with me !!!..........Uncle Sam, Pa.
     
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