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A rib w/.400 taper in height how high

Discussion in 'Shooting Related Threads' started by Dr.Longshot, Dec 10, 2009.

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  1. Dr.Longshot

    Dr.Longshot Banned Banned

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    From a 50/50 POI how much higher will a rib w .400 taper shoot, or how high does .100 shoot I would like info as it is too cold to pattern the gun.
    There is a formula out there that extrapolate this.

    Or to put it this way how much taper is required to get 4 inch pattern raise?


    Gary Bryant
    Dr,longshot
     
  2. Neil Winston

    Neil Winston Well-Known Member

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    It depends on how tall the rib is. The taller the rib, the more pitch is needed for a particular height of POI over the rib-line.

    But for practical purposes you could say that 1/32 in inch in down-pitch in the rib will result in an inch higher POI, once the three or four inches of shot-drop at 40 yards are accounted for. The height of the end of the rib over the bore centerline will also add a constant POI depression of the same magnitude, and that's unrelated to my first comment about high ribs.

    All that assumes that the gun puts its shot straight along the bore (discounting gravity) which is an assumption you make at your own peril, of course.

    Neil

    Was that _the_ Dr. Longshot whose picture we saw in the latest issue of T&F, Gary?
     
  3. wlc

    wlc Member

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    I think you could do a simple equation to determine how much an increase in pitch will change the POI. In this equation "x" is the amount on increase in pitch, "b" is the distance in inches of rib that will be changed by the pitch, "c" is the amount of change in POI desired, and "d" is the distance in inches where you want the change to occur.

    Just for an example say your rib is 30" long and that you want to raise the POI by 4" at 30 yards ( 1080")

    x/b = c/d or x/30 = 4/1080, or .111" of change in the 30" rib would change the POI by 4" at 30 yards.
     
  4. Dr.Longshot

    Dr.Longshot Banned Banned

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    Neil I don't know as I do not get T&F Anymore, where was it taken?
    If it is from the Las Vegas Fall Hdcp, I will say yes.

    I am suspecting the rib shoots a strong 100% pattern

    Gary Bryant
    Dr.longshot
     
  5. Dr.Longshot

    Dr.Longshot Banned Banned

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    Neil can Trap and Field be seen on thye computer?


    Gary Bryant
    Dr.longshot
     
  6. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    The tangent of .400 by say a 34 barrel should be over 16" high at 40 yards.
     
  7. Neil Winston

    Neil Winston Well-Known Member

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    I'll try to scan it for you, Gary.

    Let's try this another way. We'll assume a straight-shooting barrel and float a rib one inch above its centerline. That gun will shoot, at 40 yards, about 4 to 4 1/2 inches low. Three and a half will be the drop in the shot due to gravity, one will be due to the fact that the far end of the rib is about one inch above the center-line of the bore and so the shot _starts_ one inch low.

    Now let's raise the chamber-end of the rib. leaving the muzzle-end where it is, another inch above the center line of the bore. We'll start with a 36-inch rib and every inch we raise the chamber end will result in a 40-inch rise in the POI at 40 yards.

    Your 0.4 inch pitch is 40 x 0.4 or 16 inches high, so this gun will shoot about 16 inches higher than the one-inch-high and parallel-to-the-bore rib we started with. It started shooting about 4-plus inches low, so it should now shoot about 16-4 plus = 11 or 12 inches inches high. We've ignored the tricky effect rib-height by itself has, but I doubt it's much.

    If the rib is shorter, it'll shoot higher with the same pitch. For example, a 32-inch rib with the same 0.4-inch pitch would put the shot about two inches higher.

    Neil
     
  8. Dr.Longshot

    Dr.Longshot Banned Banned

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    Neil it is a 34" Bbl from the chamber to the peak of the rib is 4 1/2 inches and the rib stops 1/4"in from the muzzle. I was thinking approx. 18"in high to the center of the pattern, I think I am pretty close, what do you think?

    Which issue of Trap and Field was the pic in?

    Gary Bryant
    Dr.longshot
     
  9. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Also, when calculating POI you have to take in consideration how high the front bead is.
     
  10. Neil Winston

    Neil Winston Well-Known Member

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    You are in the December issue, included as a result of your good handicap shooting at Las Vegas. Congratulations, Gary.

    OK, one inch at the back of a 36-rib would be 40 inches at the target.

    again, 4/10 of that is 16 inches.

    But the rib, being shorter, requires a correction factor such that:

    rise of shot = (uncorrected rise x rib factor)

    rib factor = 36/29.5= 1.2 (since 34-4.4 = 29.5)

    so rise of shot = 16 x 1.2 = 19+ inches

    but then you have to account for gravity and (bore-center to rib-end - what toolmaker above calls height of front bead) ), a total of about four+ inches.

    So, by my calculations which ignores some minor (I think) stuff, this gun should give a POI at 40 yards of 15 or so inches high, which yes, I would call pretty close to your estimate.

    The warning needs repeating. This only works out close anyway, and depends entirely on the gun putting its shot right, straight down the line of its bore. It may do that, or it may not. Thus the above is no more than an estimate, a "best case" guess. Only actually testing it will let you say it shoots "there" or "there."

    Edit: One thing to remember, Gary, is that all this also depends on you sighting right, straight down the rib. If your eye is a little higher, so is your POI. A "stacked bead" view, for example, might raise the POI, roughly speaking, another four inches.

    Neil
     
  11. ScottEslick

    ScottEslick Member

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    All things be equal with 2 barrels (actually one is 32" and the other is 34"), if the rib is 1/8" higher on one than the other how much does this affect the POI?

    Thanks, Scott
     
  12. Neil Winston

    Neil Winston Well-Known Member

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    If the rib-pitch is the same, I'd estimate 1/8 inch. You can safely round down to zero if you like; I would.

    Neil
     
  13. GW22

    GW22 Active Member

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    The calculations are pretty straightforward, and are fine for an initial starting point, but all the trigonometry in the world can't tell you half as much as the patterning board.

    -Gary
     
  14. Neil Winston

    Neil Winston Well-Known Member

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    Yes, Gary, I agree completely. That's why I called it "a best-case guess." "Best-case" in this usage means "If all the other guesses and assumptions you made turn out to be right and you have a bit of luck too."

    In fact I've found surprises so often I never do any of the above; I just shoot it at crosses on paper 13 yards away off a bench, many shots over at least a couple of days - and that beats all the math in the world.

    Neil
     
  15. samiam03

    samiam03 Member

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    If you factor in raising the comb in combination with a raised rib will that lower the POI? If not - how do you lower the POI with the comb all the way down?

    Sam
     
  16. Neil Winston

    Neil Winston Well-Known Member

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    It depends on what you see now, Sam.

    1. You see a lot of rib and it shoots too high. File on the comb or

    2. You are right down the rib and it shoots too high. You are in the market for

    A. an add-on rib like Keensights or similar or home-made or

    B. a different gun.

    Neil
     
  17. samiam03

    samiam03 Member

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    Neil: as a one eyed shooter I pattrened at 100%. Forced myself to become a two eyed shooter (box and a half of shells) and need to verify how it's pattrening now. Two eyed I'm seeing a whole lot of rib when I do a quick glance to see if the beads line up. Now gun fit is crucial.

    I've scheduled some time with a coach at the pattrening board so I can remove gun fit as a varible.

    As always thanks Neil

    Sam
     
  18. Dr.Longshot

    Dr.Longshot Banned Banned

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    Neil, Now all I have to do is get one of the stocks he is sending me for a better fit, I need more Right cast-off, and hopefully a shorter stock so I don't have to cut one.

    Neil the bore on this is .750 34 inch Bbl .030 choke that starts 3 1/4 inches from the muzzle and has 1 1/2 inches of straight through at .720, hope to put it on paper when it warms up. We will see how this paralell works?

    I would prefer to have a .740 bore, but will give this a try.


    Gary Bryant
    Dr.longshot.
     
  19. Neil Winston

    Neil Winston Well-Known Member

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    Gary, you are such a darn trapshooter! You get your face in Trap & Field

    <a href="http://photobucket.com" target="_blank">[​IMG]</a>

    . . .and celebrate by buying a new gun! You haven't said yet what it is, Gary, but I'm betting Kolar. Right?

    Neil
     
  20. Jollytrapshooter

    Jollytrapshooter Member

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    Using my modeling program, a 34" rib with .400" difference in taper would shoot 12.606" higher at 30 yards, give or take a few thousandths : ) Of course as others have said, the trig isn't going to tell you nearly as much as the patterning board will. Good luck, Josh.
     
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