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Neil's POI procedure...somebody explain it??

Discussion in 'Uncategorized Threads' started by Capt. Morgan, May 1, 2008.

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  1. Capt. Morgan

    Capt. Morgan TS Member

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    I have a chance to use an indoor ballistics range tomorrow and want to try the POI thing.

    I think I have the basics: put an aim point on a large target that's set out 39 feet; bench rest the gun and fire at target; put a hole above the aim point.

    Now, here's where this loses me: how do I learn anything meaningful by putting a hole in a target that's 13 yards away when what I really shoot at is 35 to 45 yards away when I hit it? If I measure the rough center of the 13 yard hole as being, let's say, 3 inches above where I had the top of the front bead, what does that translate to in real life, and how do I make the translation for other measurements?

    Morgan
     
  2. Capt. Morgan

    Capt. Morgan TS Member

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    Thanks, 24, I'll print a copy of your reply and take it with me tomorrow.

    Morgan
     
  3. ColBuckShot

    ColBuckShot TS Member

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    I believe I understand the procedure and results of the patterning process but not what to do about it. I'm confused by what to do about the results when stated:
    Remember 'up is down' so if the POI on the pattern board is 1" high that means in real life you have to aim 1" below the bullseye.
    Doesn't that undo the pattern from being higher then the target. I mean to say a gun that would shoot 100% high if lowered 5" would now shoot flat. Is'nt a gun that shoots a 100% mean a gun that shoots its entire pattern over the POI. I know I've missed something here, please advise.
     
  4. ColBuckShot

    ColBuckShot TS Member

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    The last line I meant to say the POA point of aim, not POI
     
  5. Dove Commander

    Dove Commander TS Member

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    Shoot at least 5 individual patterns, cause you'll "pull" a couple. Actually, the only purpose of shooting at 13 yards is to make sure your gun shoots vertically dead on, (not right or left of your aim point). If it shoots left, which is common for righties, move your stock comb right at 1/16" intervals till your right on. I then move back to 28 yards and do it 5 more times and etch a line through my pattern to make sure I'm dead on. It's like sighting in a scope, the farther back you are, the more precise your pattern is, but you have to be sure your holding steady, or it's a waste of time. I shoot 5 on a bench, then 5 standinga nd see if their the same POI. If they are, I also bench rest at 28 yards to finish it up. Forget the 60/40, 70/30 stuff. When I sell a gun, I tell them it shoots X inches high at 28 yards with a figure 8 for me. The 70/30 thing is too confusing.
     
  6. Dove Commander

    Dove Commander TS Member

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    Once you know your OK vertically, go to trap range and shoot Straightaways. Adjust up or down till your center punching'em. Then shoot some normal rounds. and see if your close on hard rights and lefts. If you are, THEN GO BACK TO THE PATTERN BOARD AND DOCUMENT HOW HIGH YOUR GUN SHOOTS AT 13 OR 28 YARDS. KEEP IT FOR RECORD. I normally don't document a gun till I've shot it for a month, cause some things change once you get comfortable with the gun ( comb height and swing speed)
     
  7. Capt. Morgan

    Capt. Morgan TS Member

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    "Is'nt a gun that shoots a 100% mean a gun that shoots its entire pattern over the POI. I know I've missed something here, please advise.

    That's the whole point, Col...

    A gun that shoots flat in the hands of a one-eyed shooter is a recipe for head-lifting misses because the barrel has to cover the target at the moment the trigger is pulled. Having a gun that shoots higher than its pointed allows the shooter to keep the target constantly in view. Having a gun that shoots "just a little high" (like 60/40) requires the shooter to keep the bead directly against the bottom of the target when firing. As the point of impact rises (to something like 80/20) a bit of space is required between the barrel and the target in order to get a kill. It depends on what you like/need.

    Morgan
     
  8. ColBuckShot

    ColBuckShot TS Member

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    Capt:
    I meant to state point of aim (not POI), never the less if you lower the point of aim as many inches as in the formular stated then wouldnt a 100% gun be shooting flat and therefore counters the very point your making.
     
  9. hmb

    hmb Well-Known Member

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    It is also important to find out if it shoots to the left or right. HMB
     
  10. phirel

    phirel TS Member

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    First, 24str8 left out one important step in his explanation. He forgot to subtract the 3 inch fall of the shot due to gravity and add in three times the distance from the center of the bore to the front sight.

    The primary reason for testing at a close range is that the center of the pattern at 13 yards can accurately be determined. The exact center of the pattern at 40 yards cannot be determined without a lot of analysis or a computer assisted program.

    Capt. Morgan- Your explanation will work for a rifle, but not a shotgun. You should never try to place the front sight on or below the target. You have two choices. One is to clearly see the front sight, the other is to see the target. You can't do both.

    To shoot a shotgun, align the sights when you have the gun mounted, then focus your eyes where the target will emerge. See the target clearly (at this time you only see the front sight as a blur or not at all). The gun will move to the target and seems to shoot itself. All you have to do is see the target clearly and keep your head down.

    Testing a shotgun at 13 yards is important to determine where the shotgun shoots. It will not tell you where you shoot the shotgun.

    Pat Ireland
     
  11. Capt. Morgan

    Capt. Morgan TS Member

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    "Capt. Morgan- Your explanation will work for a rifle, but not a shotgun. You should never try to place the front sight on or below the target."

    Pat, now I'm confused again! The explanation I gave was for how I intended to conduct the POI test, not for how to try to kill clay targets.

    Are you telling me that it's not permissible to establish a relationship between the gun's front bead and the cross on the paper? I thought that was essential be getting meaningful data? Even Neil's original post on the subject contains this in the list of steps (my emphasis):

    "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.

    Frankly, I think I'm going to be better off if I just keep shooting at 40 yards like I've always done. I'm getting the distinct impression that nobody but Neil completely understands his technique and he hasn't answered the thread with less than 4 hours to go before I shoot.

    Morgan
     
  12. phirel

    phirel TS Member

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    Morgan- I guess I was not clear. Yes, at 13 yards, shoot the shotgun from a rest just as you would shoot a rifle. Be aware that you are testing the gun, not how you shoot.

    At 13 yards, point directly at a mark. Shoot at least 5 targets, 10 is better. One or two targets will shot that you pulled the gun off the target. Toss these in the trash.

    On the remaining 7-8 targets, measure the distance of the center of the pattern from the target. The center of the pattern will be very clear. If the center of the pattern is consistently 4 inches high at 13 yards, this would equate to 12 inches high at 39 yards.

    Next, gravity will lower the POI another 3 inches between 13 and 39 yards, so that now gives us 9 inches high at 39 yards. Finally, add three times the distance from the center of the bore to the front sight. If this distance is 3/4 of an inch, you would add 2.25 inches to the 9 inches = 11 inches high at 40 yards (rounded).

    For fun, why don't we try this. Shoot your patterns at 40 yards and do the best you can to find the center of the pattern within one inch. You will find this very difficult to do with any accuracy. Then shoot some patterns at 13 yards and just post your results. We will calculate the POI as determined at 13 yards. That will allow us to compare the two systems.

    Remember, the most important information you will gain is if the gun is shooting to the right or left. That is bad.

    Pat Ireland
     
  13. GunDr

    GunDr Well-Known Member

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    What I've found that works very well with patterns at 40 yds, is the use of a clear plexi-glass 30" circle, with a 1/4" hole drilled in the center.

    Using this circle, you can place it over the pattern paper, and shift it around until an even distribution of pellet holes can be seen. Maintaining an error of approx 1" should easily be attained. 10 shots and toss the "pulled" shots.

    Only using the "x-%" term can be used at 40yds. 3"=60/40, 6"=70/30, etc. These mesurements are always measured from the center of the pattern to the center of the aiming point. Many confuse this percentage term with the actual diameter of the pattern. An example would be a full choke pattern shot at 25yds. Though most, if not all of the pellet holes will be above the aiming point, this will not translate into a gun shooting "100% high".

    At times I feel we can get waaayyy overboard on the POI analyzes. After all, we're trying to point at a moving object at a distance 32yds to approx 50yds. There will always be more human error in the point, than a gun that might be an inch or two off.

    One more thing, the gun must have a rock solid rest, while attempting this "rifle" shot. Also don't get discouraged if you cannot keep from pulling the shot. Have a few other shooters take the shots. While I was patterning almost everyday at Kolar Arms, at least 50% of the shooters that came in couldn't make the shot, even at 15yds., but were deadly on a moving target.
     
  14. Neil Winston

    Neil Winston Well-Known Member

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    I admit to being confused by much of what I read above, as are apparently many.

    First, a general overview, which is a question seldom asked: "Why do you want to know where your gun shoots at 40 yards?" Seriously, why? Think about it while we do something else.

    The point of close patterning is that it minimizes outside influences (like wind), leads to easy identification of "pattern center," and, most important in my view, lets you take a lot of shots. If you just take a few, you are missing most of the value of the procedure.

    With a full choke a 36x36 (better 48x48) sheet of paper will allow 9 shots to a sheet and that's a start. Put the bead at the base of the cross and shoot, using the sight picture (that is, what you see down the gun) you generally use. I keep a record of every shot as I shoot it. You don't have to measure anything, just look and estimate. A typical record might be:

    1. An inch high and a little left

    2. Flat

    3. Just a bit high and a little left again.

    4. Higher, but a bad shot

    5. Over an inch up, straight

    6. Like the last and a perfect shot

    7. Again, an inch-plus high but this time less than an inch to the right. Jerked the gun when I shot.

    8. An inch high, maybe a bit left but not much

    9. A perfect shot. Straight and 1 1/2 inch high.

    With data like that, I'd settle on OK left/right performance and an inch or so high. And that's where I'd stop and move right shooting it to see how the scores (and other data, cited later) are. It's a reasonable POI for a start, nothing to worry about right/left, and there's not much more we can do at the bench for now.

    But say it had gone as follows:

    1. An inch high, 1 1/2 left

    2. An inch high, a little left

    3 Left again!

    4. Tried shooting right a bit and the POI was about centered on the cross but a bit high.

    . . . Well, you get the picture. It's shooting left for me today. So now I put the gun up and really, really check on what I see. Am I looking straight, straight, straight down the gun? Put that in the notebook. You might suddenly see, as I did testing my new MX-2000, that while I was fiddling with the comb my eye was moved off the centerline of the rib and I'd shot a few rounds of trap and several shots off the bench and never noticed. If something can be moved to get me down the rib again I'd do it and start a new series. However all this comes out, if I suspect a problem I'd finish out the nine and come back another day and see it it happens again. Let's say it does:

    My standard for OK horizontal deviation is maybe an inch at 13 yards. Whenever the hole made by my full choke touches the vertical line I call it straight, even though it may fade a bit to one side or the other. If it is two inches off I don't shoot it. I _don't_ think moving the comb will fix what the gun has, a fatal defect. Fix it or sell it; preferably the latter. But before you banish it, get a second opinion or two. Have another shooter and his friend do the same test - fewer shots of course, but just see if the flaw is reproduced by others. If not, then it's more "think time." If it is, the gun is, until fixing, a junker.

    Getting back to vertical displacement from the point of aim, let's go way back to the beginning. First, a simplification which will work unless you have some kind of - currently, if perhaps temporarily, popular - "high rib special."

    Assuming it's a inch-plus or so from from the top of your muzzle-end bead and the centerline of the bore, you can just take the displacement of the POI from the POA, multiply by three and be done with it, to the accuracy required (if any - more on that later.) That's zzt's program, assuming I read it right, and I think it _is_ the easy way.

    Or you can do analysis of what's happening. The shot starts at the centerline of the bore and goes (to the accuracy required) straight to the place it hits on the paper cross at 13 yards. (OK, it falls 0.2 inches but we are going to ignore that.)

    Warning: I've changed my mind about this next paragraph; this is "old-speak" which will be corrected in later paragraphs.

    So say you have a big-rib gun and it's two inches from the centerline of the bore to the top of the bead. And it hits an inch above the cross. So on the way to 13 yards it rose three inches, over 40 yards it will rise 9 inches. Correct for the fall due to gravity, three (plus) inches and you have a gun which shoots 6 inches high at 40 yards.

    That's the way I've advocated doing it, but a lengthy tread a while ago lead me to refine it. Correct it, that is.

    The above analysis makes a mistake. Yes, the shot has risen three inches but when we do as above, we do not take into account that we now have a new "starting point," that hole an inch above the POA. If the shot rose three inches in 13 yards, it will rise an additional (to that one-inch high hole) six inches in the next 26 and so the point we should make our "gravity subtraction" from is not nine inches, but seven. I'll leave it to the student to derive this another way as a proof. Show your work.

    So now we have a gun which shoots straight horizontally and four inches high vertically. And we'll finally get back to my opening questions. "Why do you want to know where your gun shoots at 40 yards? Seriously, why?"

    There's only one reason I can think of, to compare two guns with different rib-heights whose results might mislead you (regarding 40-yard POI) if you weren't careful with your 13-yard math. But beyond that there's not much "there."

    You can't think you need "an 80/20 shooter." You don't know what you need until you try it and once you have it where you want, the fact that it is such and such is just nice to know but will not change your score. Remember, you know where your gun shoots and almost no one else you talk to knows where his or her gun shoots ad so what can you learn from them? Particularly, avoid anyone who actually says "80/20" or "100% " since if they had ever tried to find out they would almost surely say "10 inches high."

    You can't translate this into any "bird-rise" formula since they are not much related to shooting if they even work at all which I doubt more and more.

    So what are we to do with "vertical displacement?" Maybe we should just take Dove Commander's advice. Make the gun shoot right vertically by tracking smoked birds and scores, _then_ determine POI and keep it handy for the next gun you buy.

    One problem with determining "suitable POI" by shooting is that there are (at least) two ways to shoot trap call them "aiming" and "not aiming." Both work for singles, maybe only "not aiming" works at handicap but I've never been able to find out. The trigger-timing for the two techniques is so different that a vertical POI that works of one will not work for the other. So when you go out to move the POI unless you use the same technique then as you do really shooting, the results won't work.

    I like to get a POI which smokes a lot of birds. I ignore anything about "reading breaks" since I don't believe in it. I you really are someone I read posting here so often "I never see the gun at all" then you are just stuck with trusting the score (and puffballs) and so lose a very helpful datum, missed birds and mis-pointed birds. To make it work, you need a technique which tells you where the gun was when it went off, if only very generally.

    1a. Mis-pointed high and a miss. No information.

    1b. Mis-pointed high and a good hit. Begin to consider a higher POI is this happens often.

    2a. Mis-pointed low and a miss. No information.

    2b. Mis-pointed low and a good hit. Begin to consider a lower POI is this happens often.

    The above refers to serious mis-points. If the gun sneaks a little high or low and gets a piece anyway, than I think that we should go after a mid-point. That is, both a little high or low should get a piece, not just, for example, low OK with no score if the gun gets even a little high.

    We'll that's a start at least, Capt'n.

    Neil ©2008
     
  15. GunDr

    GunDr Well-Known Member

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    Neil,

    If your saying that using the 40yd standard is obsolete (from the the old industry standard), why reference the 13yd test to 40yds, as you do?

    I guess I was lucky that for most of my past patterning experiences, were done indoors (no wind) and a solid rest. At the 40yd testing, true..the human error is greatly exaggerated (with a poor shooter), but a confident shooter, can see more clearly the "faults" in the gun.

    Doug
     
  16. Neil Winston

    Neil Winston Well-Known Member

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    I don't, Doug. You know Minnesota and the chances that on the day you can pattern there will be zero wind. I only think of 40 yards if the experimenter wants to know. I just stay with 13; it tells me all I need to know, POI-wise.

    I do my patterning at 40 or 34. Because they are industry standards, just as you say. However, I don't believe I can "see" the faults of any gun at 40 yards.

    1. If the fault is side-shooting I can see that better at 13 yards.

    2. If the fault is pattern, I can't "see" it. I can count it.

    Neil
     
  17. Capt. Morgan

    Capt. Morgan TS Member

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    "For fun, why don't we try this. Shoot your patterns at 40 yards and do the best you can to find the center of the pattern within one inch. You will find this very difficult to do with any accuracy. Then shoot some patterns at 13 yards and just post your results. We will calculate the POI as determined at 13 yards. That will allow us to compare the two systems."

    OK, here's what I ended up with today...

    I used my light full choke (Invector Plus, .028" constriction) in the bottom barrel of my XT. I have a full choke but I don't use it and I wanted to conduct the trials with a choke I actually use on the off chance the full (.035") didn't shoot where I know the LF shoots.

    I shot at 3, 40-yard targets, 3 shots each of new STS 2 3/4 DE, 1 1/8 oz 7.5 shot. I shot 2 from a bench rest and 1 off-hand. All 3 targets show that the pattern is the most dense at about 8 inches above my aim point.

    I shot 10, 13 yard shots using the same loads, same choke but all from the bench. Throwing out the 3 that went a bit off, I got 7 shots that cut the vertical line to some degree. The center of the biggest hole in each trial was generally ±1 1/2 inches above where I placed the top of my front bead. The top of my front bead is 1 13/16" above the center of the bore of my bottom barrel.

    So, how do the two procedures compare?

    (BTW, it's going to take me a long time to live down the abuse I took for shooting a long gun at a target 39 feet away. I can't repeat most of what was said, but I can say for certain that no one I was with today had anything complimentary to say about the process.)

    Morgan
     
  18. Neil Winston

    Neil Winston Well-Known Member

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    Let's do the math, as they say on the business show on NPR.

    To get to 1 and a half inches high at 13 yards from a start at 1 13/16 lower than the POA, the shot rose 1 13/16 plus 1 8/16 which is 2 and 21/16 or 3 5/16 inches or 3.3 inches. Since we are being so careful - measuring to the sixteenth - we will factor in the 0.2 in drop on the way to 13 yards, giving us a total rise of 3.5 inches. From the 13 yard line to the 39 the shot will rise another seven inches, which added to the start of i 1/2 is 8 1/2 inches. Subtract the three inches of gravity fall and you get a predicted POI of 5 and a half inches, which is two and a half inches lower than you observed. That's not as close as I generally get, but good enough to place your gun as one which shoots moderately high. Are you satisfied with that degree of agreement, Capt'n?

    Neil
     
  19. Capt. Morgan

    Capt. Morgan TS Member

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    "That's not as close as I generally get, but good enough to place your gun as one which shoots moderately high. Are you satisfied with that degree of agreement, Capt'n?"

    Well, it tells me that the gun hits higher than I point it, but I already knew that. It also tells me that I have to stay tighter to the targets now that I have to wear this dot than I thought I was staying when I didn't. It tells me that the gun shoots a bit higher than "flat" but a bit lower than Harlan Campbell's.

    The 40-yard shot are the wild card. Thinking about it now, I probably should have shot 9 individual targets 1 time rather than 3 targets 3 times because just 1 slightly-higher shot out of three will be enough to raise the apparent pattern by an inch or 2.

    I may try the test again with the full choke to see if that makes it any easier to define the location of the core of the pattern. Am I satisfied with the degree of agreement? I won't say it made me want to give up shooting 40-yard patterns, but it IS a useful diagnostic for gun performance. If I can remember how to do the math, I'll continue to use it (despite what my buddies said).

    One thing I am curious about though is whether there would be any meaningful difference in shot drop if smaller or larger shot was used for the tests...not because of the effect of gravity but because of the difference in the effects of wind resistance on the smaller or larger pellets?

    Morgan
     
  20. phirel

    phirel TS Member

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    Morgan- Think about the abuse you would have gotten shooting a target from a rest at 13 yards and missing it.

    Absolutely, shoot only one shell at each target. I like to use numbers and the method Neil has given us. But, the real key is figuring out what the numbers actually tell us. Most important, the 13 yard test will accurately demonstrate if the gun is shooting to the left or right. That is important. Next, I believe the numbers will tell us if our gun is shooting flat, a bit high or very high.

    Patterns are so irregular, I have come to the conclusion that designations such as 60/40 and 70/30 are nonsense. Patterns cannot be measured that accurately.

    Pat Ireland
     
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