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Is effect of cant greater w/ high ribs? (Winston)

Discussion in 'Shooting Related Threads' started by Neil Winston, Dec 15, 2009.

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  1. Neil Winston

    Neil Winston Well-Known Member

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    A few days ago, another “gun canting” tread showed up, connected with the shooter’s move to an unsingle. And the result of the shooter’s idea that he was missing because of cant was as usual. Lots of advice, lots of opinion; mostly, it seemed to me a lot of “explanatory fictions” that are somehow so effective in cyber-coaching. Somewhere in there languished a post by me which said canting is not his problem, what the magnitude of the effect is, how to calculate it, and what the small POI deviation is determined by; you know, the same old line I’ve been pushing for a couple of years.

    But this is a little different. There have been at least two recent revivals in print of “high-ribs sensitivity to canting,” in contrast to the trustworthiness of our old guns, the ones we all used to shoot. And I’ll admit right now the fact that high-rib guns are more affected by cant is self-evident. All of us can, in our minds, pick up a Pro-Rib Whatever, tilt it a bit, and see that the shot is going to be sent way off to the side because of the high rib.

    Let’s turn the clock back a couple of years, when the same sort of thing was in the press and in the minds of many shooters. I noted then (as I do now) the lack of any specific numbers attached to any of the pronouncements by experts. Who did you ever read or hear say “If the rib is two inches high and the tile is such-and-such, the shot will be moved to the side by NN inches.”

    Well, I hadn’t read or heard it either, but it seemed like a trivial geometric problem which would at least give me some numbers, which is always my first stab at deciding if something is worth worrying about or not. But when I tried, the solution kept slipping away. First went all the “axis of rotation” considerations, soon thereafter, the rib itself. I decided, finally, it was solely related to the point-of-impact (POI) in relation to the point-of-aim (POA) and that was the case I made on that thread. I also gave my guess: the deviation to the side is the product of the sine of the angle of cant times the height of the POI over the POA.

    I had no proof of this, but when you need a multiplication factor which starts at zero at 0 degrees and goes to one at 90 degrees, sine is just begging for consideration. Likewise, I said later (as a result of a comment by zzt) as you cant a gun the POI is depressed by a multiplier which is the cosine of the angle of cant, but this is not really symmetrical with the horizontal effect because you have to consider gravity and it’s hardly worth it, except to see if you are right.

    A year later we went though the whole thing again here in TS.com, but since I’d lost people the first time, I dragged it on, pretending I didn’t know the destination so I could better show the step-by-step route to my goal.

    I can’t say I made much progress that time either. It’s something you have to think really hard about and you have to call false something that is obviously true, so my converts were few; maybe there weren’t any at all.. After all, as so many intone here, “talk is cheap.” OK, I_ don’t know what that means, but in this case it seems to have meant “If you can’t convince me in ten words, I’ll just go with what I’ve always believed.”

    So here we are, once again. This time I’m going to show you, not just tell you.

    Our text is from Trapshooting USA, volume two, page 46 (thanks to Smok’n Joe for bringing it to my attention.) Alan Rhone writes, in the article “Another bad habit”:

    “The trap game today is dominated by high ribs and patterns shooting over 100% high are favored by many. Two additional factors that can cause problems for our gun canter. A rib that sits high over the barrel magnifies the effect of cant and if that rib is elevated sufficiently to place the pattern 100% it adds to the problem.”

    OK, Alan’s got it backwards about the relationship between high ribs and POI (a high one, if the pitch is the same, will shoot lower) but I think we all understand what he’s getting at and the high-rib part really couldn’t be more clear.

    OK, let’s get rolling, This time I’ll try to prove it with pictures, not words.

    Here’s the setup:

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

    The base is an old Palmgren angle vise, the king of the toolroom before multi-axis CNC machining centers, but still up to any number of one-off tasks. Above it is the gun with two ribs. OK, they look like laser pointers and they are, but for our purposes, it’s a gun with two stacked ribs.

    The lower pointer is the barrel and it shoots its green laser light just as it would shot (neglecting gravity.) Where the green light is, that’s where the shot is. The laser-pointer is on a pivot so we can make it shoot as high as we want, independently of the other two pointers.

    Next above, an inch above the green “shot” laser, is the “low rib” pointer. It project a red laser beam to the target, as does the one three inches above it. That upper one is the high rib, just like the low rib but above it; think “high-rib gun” and you will get the image..

    Though you may miss the hardware, I think you can see that this exactly what we are talking about when we discuss high- and low-ribbed guns: a shot-line, a low-rib line and a high-rib line.

    Here’s the target sheet we’ll use to see where we are pointing

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

    The intersection of the two black lines at the lower right, that’s the target. Let’s hit that target dead on; here’s our green laser, the shot, hitting the target.

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

    Now we’ll introduce a flat-shooting, low rib; the added light is from the lower red laser pointer.

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

    Now the red pointer representing the high rib:

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

    And all together: the green shot and to two red lasers, one being the high rib and the other the low. This is a gun that shoots dead flat, and both ribs are built to give that desired flat shooting. And you can see, all the lights, two red, one green, converge to smoke the target, the intersection of the two black lines.

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

    We’ll leave that for a while, what’s going on will become clear soon enough. We think we need a higher shooting gun. This is trap, after all, and “all the targets are rising.” This is easy with this setup. The green laser is pivoted and we just move it up, four inches in this case. Since the laser-to-graph-paper distance is 17 feet, the “real-world equivalent is 4 x (120/17) or a pattern 28 inches high in handicap terms.

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


    Now let’s tilt the vise 30 degrees. This is a lot in the canting world, but we want a big effect, don’t we?

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

    Oops, now we aren’t shooting at the target anymore, the intersection of the black lines:

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

    No problem, we’ll jog the mill table around a bit and start with just the low-rib laser, pointing again at the target. This is, after all, what we do when we shoot. No one has ever said that when we cant a gun we quit shooting at the target too, have they?

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

    And now switch on the green shot laser and I think we get what we all expected, a high, left shot. Here’s the low rib result with the red dot on the bird, the green dot being the shot.

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

    But, here finally, is the critical test. What’s the relationship between the high-rib aim point and where the shot goes? (drumroll while we switch on the high-rib laser to join its low-rib partner)

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

    So that’s it. When they are pointing at the same thing, both high and low ribs move the POI the same amount to the side when the gun is canted. In other words, there is no “greater sensitivity to cant” for high ribs, it’s all in how high the POI is over the POA and is unrelated to rib height, no matter what you may have heard, read, or what seems obvious.

    Oh yes, remember the “numbers” concern I started with? Why you haven’t read any predictions except mine, and mine were unproven.

    Well, now they are, if not proven, at least supported.

    1. The big squares are inches

    2. The shot started four inches high.

    The tilt is 30 degrees and and the sine of 30 degrees is one half. So if I’m right, the shot should move two inches to the left.

    And Look! It did.

    So I’ll say it again, with a little more confidence this time. If you want to know about the effect of cant on the horizontal displacement of your shot, forget about ribs and figure from the distance between your POA and your POI. Take the cant in degrees, find the sine, multiply that by the vertical POI (and the result won’t be much, hardly worth all this, all in all.)

    Thank you for your attention. Neil

    ©2009 Neil Winston
     
  2. JACK

    JACK Well-Known Member Supporting Vendor

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    You are welcome.

    And thanks back to you as well.
     
  3. phirel

    phirel TS Member

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    Neil- Thanks for clearly illustrating what many, most I hope, realized. What a few posters seem to have said is that if a high rib gun and a low ribbed gun both shoot 12 inches high at 30 yards, the gun with a high rib will shoot higher at 30 yards. Not the best logic I have seen. If both guns shoot 12 inches high at 30 yards, and they are rotated 90 degrees clockwise, both will shoot 12 inches to the right.

    Your three barrels shooting three different colored lights is ingenious. Thanks again. I understand your protection of some of your better posts and I expect an autographed copy some day.

    Pat Ireland
     
  4. Dr A C Jones

    Dr A C Jones Member

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    That is indeed impressive.

    Andrew.
     
  5. hmb

    hmb Well-Known Member

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    Final conclusion, the positive effect of canting the gun inorder to place the rib and beads infront of your aiming eye, while keeping your head and eyes straight and level, out weighs negative effect of shot displacement. HMB
     
  6. zzt

    zzt Well-Known Member

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    Neil, as with the previous thread, your conclusions are only true for the fixed distance the gun is "zeroed" at. You are dealing with angles, not parallel lines. They may converge at one point (zero distance), but at any other point they do not. The larger the angle (higher rib), the larger the discrepancy at any other distance. You can demonstrate that with your imaginative rig.
     
  7. Smok'n Joe

    Smok'n Joe Active Member

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    Neil,

    Brilliant illustration!

    Clear and concise explanation of my observation...THANK YOU!

    You are absolutely correct in asserting that the effect of GUN CANT that I eluded to in my original thread is a function of the difference between the POINT OF IMPACT and the POINT OF AIM, and not the height of the rib.

    To further illustrate your arguement, I own a Mossberg AHT that I puchased out of curiosity almost 30 years ago. The gun came equiped with a hideously high Simmons Olympic Rib, but it shoots flatter than an 870/1100 field gun. To this day I wonder about what the intended advantage of the rib design was. I reference that gun because the POA and POI are dead on when the target is 100% covered. Therefore, I am either NOT CANTING that gun, or as you propose, and I agree, any effect of canting is negliable.

    However, I think you will agree that the design intent of a HI-RIB SINGLE or UN-SINGLE trap gun is to RAISE the POINT OF IMPACT over the POINT OF AIM, which therefore creates the potential for CANTING distortion and that the effect is further exagerated as a function of the height of the POI, i.e., canting a gun that shoots 100% high is subject to more distortion than the same gun that is set to shoot 60% high.

    Now I'm begining to understand why some people CAN'T shoot an Un-Single...

    Smok'n Joe
     
  8. CalamitySJ

    CalamitySJ Member

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    Neil, thanks for this, it really helps.

    Enjoying your retirement from the MTA BOD, I wonder? Like a kid in a analytical candy store.

    CSJ
     
  9. AveragEd

    AveragEd Well-Known Member

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    I saw it but still can't grasp how an unsingle or high-rib barrel won't shift the POI more than a low-rib barrel when canted. If the bead is the axis of the cant, the higher above the muzzle the bead is located, the farther inward/outward the muzzle will be rotated.

    Right?

    Ed
     
  10. Smok'n Joe

    Smok'n Joe Active Member

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    Subject: Gun Cant
    From: Neil Winston
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    Date: Mon, Dec 14, 2009 - 09:09 AM ET
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    Forget cant as the cause for many misses. It's not a strong enough effect.

    Maybe you just don't need a high-shooting gun. Do you _know_ the 1100 shoots flat and how do you know that? Do you know where the un-single shoots and if it's different from the 1100, do you know why you made that change? The fact that higher points of impact are so popular here is not a "reason."

    Last, some people can't shoot un-singles. I can't and maybe you can"t either.

    Neil

    Smok'n Joe's Reply to Neil Winstons Post:

    "Forget cant as the cause for many misses. It's not a strong enough effect."

    Per Neil's illustration, I agree the effect of GUN CANT is a function of the POI vs POA...the effect of the height of the rib over the barrel is neligable.

    "Maybe you just don't need a high-shooting gun."

    The issue is NEED vs. WANT...

    "Do you know why you made that change? The fact that higher points of impact are so popular here is not a "reason."

    Yes...I purchased the 85TSS Un-Single to improve the visibility of the target. The objective is to float the target OVER the POA which enables the shooter to focus on and read the break without having to drop the gun...

    "Last, some people can't shoot un-singles. I can't and maybe you can"t either."

    One step forward...Two steps back...

    Neil, You may very well be right!

    Smok'n Joe
     
  11. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    That is exactly how/why Joe Kuhn was able to break 99s with his Holo-Sight mounted 4 inches above the barrel. I hope some of you guys responding to this thread recall what you said when Joe posted a picture of his "out-of-norm" shotgun? Neil,Pat and Average Ed said they doubted he'd ever break a 25 with such a contraption?

    Thanks Neil for sharing your work, good job.

    Hap
     
  12. dverna

    dverna Active Member

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    Unfortunately, not all the images came up on my computer. The last two are a box with an "X" and the words photobucket - if someone can assist I would very much appreciate it.

    Neil, I tried unsuccessfully to argue this at the club. I am an engineer and I did it the hard way, using sketches and trig. Naturally, no one could/would understand it and I gave up. It is next to impossible to use mathematics to prove something to people who do not understand mathematics - especially when the theory is explained by someone like myself you is not good with words.

    Your approach is well thought out. Only a blind man cannot follow it. Yet, I am sure there are some who will declare you have missed something and the world is indeed flat - as anyone with "common sense" can see.


    Thanks for posting this.

    Don Verna
     
  13. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Is the fixture thats holding the 3 lasers dead center with the rotational axis of the tilting vise?
     
  14. zzt

    zzt Well-Known Member

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    Ed, because Neil superimposed all three dots, the illustration is misleading. Line of Sight is actually the constant here. Using that as the basis for comparison, the LOS-bore centerline angle is different for the low rib and high rib, and that compensates for the rib height differences at that one distance. At other distances, the higher ribbed gun has a more pronounced effect.

    The two "guns" are zeroed at 17'. Think air rifles here. Zero an iron sighted (low rib) air rifle at 17', then do the same for a scope sighted (high rib) air rifle (1.5" above bore). Would you expect the POI to be the same at 10 meters? No, you wouldn't, because that is impossible.
     
  15. AveragEd

    AveragEd Well-Known Member

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    Agreed, zzt. So then, cant DOES result in more POI movement as the distance between the bead and bore increases?

    Ed
     
  16. phirel

    phirel TS Member

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    zzt- I am contemplating your point. But, now in my mind, assuming the low rib and the high rib are parallel with each other, in relation to the centerline of the bore, I am not ready to concede to your point, but I am thinking (as best I can).

    Hap- Yes, I looked at the "thing" Joe developed and I did not think he could shoot it. I forgot to factor in that he must be a better shot than I am.

    Pat Ireland
     
  17. Neil Winston

    Neil Winston Well-Known Member

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    zzt, it's not misleading. While it is true that this particular setup - which is to say, this unique combination of angles - only works at 17 feet, there is no difference, in principle from this to any shooting distance you choose.

    Let's take a gun that shoots pretty high, like yours. It will shoot higher at 40 yards than 34. Does that mean that its POI is "misleading" at 34 yards. No, it's just the place it shoots at 34 yards, and where it hits at 40 is where it hits at that distance. Because the effect of cant is dependent on how "high" the gun shoots, the effect of cant will be different between those two distances as well.

    But here's the point. let's go out to 40 yards and with a canted gun, measure the horizontal displacement of the point of impact. Can you, from that number, fix the height of the rib? And what does it mean if you cannot?

    Yes, the various lines are not parallel They are not parallel with any gun except the ones that shoot at least 3 1/2 inches low at 40 yards.

    Neil
     
  18. wayneo

    wayneo Active Member

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    Neil is showing a bore, a flat shooting 50/50 rib, and a high shooting 100% rib, which in this case is exaggerated to 4" above the other rib. If it wasn't raised up, it would only be about a 1/2" above the bore light. Hard to see the effect with a 30 degree rotation.

    While the green light is a RAY since the zero stayed the same, (both ray and zero are infinite) in a 3D plane the high rib light (RAY) moved: Y/X = -0.5-0/-2-0 = -0.5/-2 = 0.25. That is what it would be a 40 yards, ie. 2" left, 1/2" low. Wayne
     
  19. Neil Winston

    Neil Winston Well-Known Member

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    Average Ed, if "cant DOES result in more POI movement as the distance between the bead and bore increases" why didn't it here?

    Neil
     
  20. Hap MecTweaks

    Hap MecTweaks Well-Known Member

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    Pat, when Joe came along with his idea, he wasn't a good shot with any kind of gun, all he had was the idea! I think a 14 or so was his highest score at the time??

    "Hap- Yes, I looked at the "thing" Joe developed and I did not think he could shoot it. I forgot to factor in that he must be a better shot than I am."

    How the the "aiming" or pointing devise or "thing" is set-up in relation the the bores centerline isn't the important factor at all, within reason. If your set-up is regulated to break targets at 36 yards, it certainly will work from 30 or 42 yards on clays. I think I saved those posts somewhere.

    Hap
     
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