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Revisit - Strange Mathematical Question

Discussion in 'Uncategorized Threads' started by dmarbell, Mar 4, 2007.

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  1. dmarbell

    dmarbell Active Member

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    In a previous thread about geometry, trigonometry and the madness of crowds, I asked a question about POI and comb height changes. My assumptions were wrong, with regards to shooting, not necessarily regarding mathematics.

    We decided, I believe, that a change in comb height of 1/16" at the comb changes the pivot point, which is the front sight on the barrel, 1/16" and the impact on POI is about 1" at 16 yards. The actual impact depends on the length from the eye to the end of the barrel, which varies with barrel length, type of gun, etc.

    But 2" at 35 +/- yards is a good estimate, and a good rule of thumb. Let's use that as a starting point, and a given for this question, please. Also, I have not patterned this gun yet, so let's ignore that deficiency and assume the Browning manual is correct.

    The manual for my newly acquired Citori Plus with adjustable rib says the POI is adjustable from 3" above POA and 12" above, with 6" being the factory setting. It was set to the 6" setting, with the front of the rib "down" and the back also "down."

    I shot 5 rounds of 16 yards Saturday, and tried to float the bird above the rib somewhat, without success. I got good breaks when the front of the barrel covered the bird. It could be a mount issue with me, but that's where my eye is looking.

    I raised the back of the rib to maximum, which should be 12" POI above POA.
    12 divided by 2 = 6. If 1/16 = 2", then 6/16 = 12". 6/16 = 3/8.

    So, in theory, to center a bird based on the above, could you mount the gun with the correct "figure 8," place something 3/8" above that sight-line and aim that figure 8 + 3/8" sight-line at a stationary bird? Is that the correct picture you should have at the end of the barrel, for vertical allowance, based on the above?

    Another thing that brought this up was a look at Terry Jordan's wall chart. The horizontal allowance was self-explanatory. For a gun that shoots 12" high, I couldn't get the bead perspective to match what my novice brain was telling me should be the vertical picture.

    Maybe for a new shooter, the 12" high number is not the best one to learn with? Any opinions on that issue?

    Danny
     
  2. Jim101

    Jim101 Active Member

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    Danny, Did you adjust the comb hight after adjusting the rear of the rib???





    Jim
     
  3. halfmile

    halfmile Well-Known Member

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    Jim, good question.

    You have to decide first how you will achieve your objective. If you raise the rear of the rib but don't move the comb to get the sight picture you previously had, you are pissing in the wind. All you have done is confuse your brain.

    Decide the bead configuration you want first, be it stacked, figure 8, or whatever and go from there.

    Shoot patterns from a rest like sandbags on a picnic table, at about 15 yards to determine POI, 34 for pattern testing.

    My friend drove himself nuts with a plus gun adjusting it to hell and back, and finally changed to a 90T with a comb. Now he's shooting great.

    to each his own.

    HM
     
  4. dmarbell

    dmarbell Active Member

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    Jim and HM,

    Yes, I raised the comb enough to give me the bead configuration I had before the rib adjustment, which was figure 8. It looks like the comb is up about 1/8", didn't use a gauge or accurately measure.

    Now, back to the sight picture at the end of the barrel.

    Danny
     
  5. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    It will "LOOK" the same but shoot higher. Hap
     
  6. chipking

    chipking TS Member

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    Heres where we stir up a S**T Storm. Danny your math is correct but you are attacking the problem backwards. There are ONLY 2 things adjustable that are important. Your Eye and the front bead all else is BS. Put tape over the center bead. From a rest adjust the comb to change your POI to where you want it using just the front bead and the bird sitting where you want it on that bead. Always place your head on the stock the same way. Try to completely ignore the rib. When adjusting the comp Up is up and right is right for POI. Once you have the POI than uncover the middle bead and adjust the back of the rib to get the sight picture that pleases your brain. Do not adjust the front of the rib unless you cannot get the sight picture you want. If you must adjust the front then start all over again with the comb and the middle bead covered to get your POI back where you want it. A rough rule of thumb is that you move the comb the same amount and the same direction as you must move the front bead to retain the same POI.
    --- Chip King ---
     
  7. buzzgun

    buzzgun Member

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    see the bird, shoot the bird
     
  8. halfmile

    halfmile Well-Known Member

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    These figures of 3", 12", etc are of necessity at some certain distance from the front sight, I assume.

    If you change that distance of course you will change the aformentioned figure.

    Each adjustment you make should be accompanied by verification at the pattern board. To do otherwise is an invitation to madness.

    I firmly believe Browning discontinued the Plus guns because they figured they had driven enough people crazy.

    Seriously, good luck.

    HM
     
  9. Harold

    Harold TS Member

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    I believe your math is correct but what's the point? First of all, it will be impossible to judge the distance to 1/16 of an inch out at the end of your barrel. Secondly, to make such an estimate, you have to be bead checking which is not a good thing. Third, the idea of shooting a gun with a high POI is so that you can point right at the target.
     
  10. phirel

    phirel TS Member

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    I use both the mid bead and front sight when I mount my gun but when the bird is in the air, I have a straight line between my eye and the bird. The front sight is simply a blur and even my limited brain somehow gets the front sight in the straight line between my eye and the bird. I have to trust my instincts and let the gun shoot the bird.

    I want my gun to shoot where I am looking, I do not want to look where the gun is pointing. I could care less if the mid bead is a figure eight with the front bead or if I see 1/2 space between them.

    The math behind POI/Sight picture/comb is interesting, but as Harold pointed out, we lack the ability to make accurate measurements with just our eyes. It is useful in setting up the gun, but not when shooting the gun. I will make POI adjustments now and then, but I have to shoot around 2,000 targets to evaluate the affects of the change. The units of measurement I use when changing POI is the "screw turn". I have gone as much as 7 screw turns up. I do not have a clue how many screw turns = one inch.

    Pat Ireland
     
  11. hmb

    hmb Well-Known Member

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    Pat,

    It is very important to know how many screw turns = an inch. This way you will know when you are being screwed. If the screw you are turning is a 6x48, then it will move 1 inch per 48 turns. The 6 is the diameter of the screw. Please store this information in your brain for future use. HMB
     
  12. dmarbell

    dmarbell Active Member

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    Harold and Pat,

    I realize I can't make adjustments while in the act of shooting. I'm trying to get an idea of what the picture should look like at the end of the barrel. I should have been more clear about the question. My intentions are to, perhaps, use the Wall Chart for training.

    Can the Chart be used by shooters of different guns without adjustment in the POA? http://www.learntrapshooting.com/leads.html Look at the Chart. It doesn't look like a gun shooting 12" high on these bead positions will be optimal. (To be fair, I don't have the chart or the instructions.) I certainly don't want to groove the wrong sight-line.

    I also realize this discussion is premature without proper patterning of my gun.

    Danny
     
  13. Neil Winston

    Neil Winston Well-Known Member

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    You are getting ahead of yourself again, Danny. You read the instructions on where it was supposed to shoot when you got it, and went from there. The thing is, you can't trust what you read. Not even close.

    Before you decide where it shoots, you have to _test_ where it shoots. As you've read so often here, 13 yards is a good place to start, and off a rest is the only way to do it and with a lot of shots and a notebook at hand.

    With those data in hand, then, and onlly then, can you go back to shooting with some number of inches in your head, but you will find, with experience, that the number itself becomes less and less informational, and will fade, over time, to no more than pretty flat, a little high, or pretty high, which is about all your eye can understand.

    Get out there to the pattern frame and tell us what you find out. We're interested.

    Neil
     
  14. halfmile

    halfmile Well-Known Member

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    Pat, you describ the subconscious act of shooting perfectly. "Let the gun shoot the bird."

    This is what I call "the little guy behind your eyeballs". He is your subconscious. When you first drove a car you were SO attentive, your feet trembling on the pedals, when the car moved an inch you jerked it over a foot. 6 months later you drove with one arm around your girlfriend, and could talk to people in the back seat, well you get the idea. You had turned over the chore of driving to your subconscious mind.

    You have to let the little guy do his job,. When I am shooting badly I usually am using too much conscious control. When I relax and let the little guy do his job it works much better. (Let the gun shoot the bird).

    This is why it takes a while to shoot a new gun well, Mr. Little has to learn it.

    If shooting was 100% conscious activity you would have it down after 1 round. Of course this is all just my take on the whole mess.

    HM



    HM
     
  15. phirel

    phirel TS Member

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    HM - I would agree, that in my case, the guy behind my eyes is indeed a little guy.

    Pat Ireland
     
  16. dmarbell

    dmarbell Active Member

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    OK, OK, I'll pattern the gun, and then we'll rejoin the discussion.

    I do have questions on patterning a trap gun, especially about the 13-yard POI part, since I have all your experiences to glean. When shooting from a rest, do you suggest I still sight a figure 8 bead configuration (which is my preferred sight-line so far)? And then, suppose I mark a circle with an "X" thru the center. Do you start by covering the center of the "X" with the front bead?

    At 13-15 yards, are you going to get enough POI change to easily see the differnce? Theoretically, a gun shooting 12" high at 35 yards should be 4-5" high at 13-15. Does that sound about right?

    I guess these are esoteric questions. As long as you know where you are pointing the gun, you can measure the POI from that consistent point.

    Danny
     
  17. Harold

    Harold TS Member

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    Danny,

    I am not an expert on the use of the wall chart, but I think what you want to do is put the bead vertically right on the target, no space between the bead and the target. If this doesn't work when you shoot real, moving targets then you would have to make an adjustment to your comb and adjustable rib, as required.

    When patterning on paper it doesn't matter if you cover the target with the bead, or have the target touching the top of the bead, just so you do it consistently. Your calculations sound about right except if you have a high rib, and/or shooting the bottom barrel you would have to allow for the fact that the line of bore is starting an inch or two, or whatever it is, below the line of sight. Also there will be several inches of drop at 40 yards due to the effects of gravity.
     
  18. whiz white

    whiz white Strong Supporter of Trapshooting Banned

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    ChipKing and Buzzgun are dead one.

    I've shot for 30 years and not sure I could "float" the bird on my bead... hell I never see the bead until after the shot, if I put my mine to it.

    You should be shooting instinctively... with two eyes I hope.

    Just go out and shoot, and shoot, and shoot.

    WW
     
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