Range Report The effects of side to side cant - field test/pics

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Brasscow

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    • Nov 27, 2009
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    Iowa
    #1
    This place is full of differing opinions on how canting your rifle side to side affects your point of impact down range. For my own peace of mind I decided to test my hypothesis. For your benefit I documented and am posting the results of the test.

    I drew up a file in autocad with 1" thick bars running horizontally across a 36" wide piece of paper. The top bar was canted 5° right, the middle bar was level, and the bottom bar was canted 5° left. My intent was to match my reticle to the thick black bars (thus canting my rifle 5° left or right) and to use the 6" orange circles in the center for my aiming point.

    The top left aiming point was to get my zero. The top right was to run a 5 round test group after verifying my zero so I knew whether or not I could proceed with the test. I wasn't going to go ahead if I was shooting like shit... this target has been riding around with me in my truck for three weeks waiting for a good opportunity to get pasted.

    Test platform:
    AI AE mkII - 24" barrel
    Atlas Bipod on AI Spigot
    Premier Heritage 3-15x50 on AI 45MOA base/rings
    Sight height over bore = 2.3"
    Load: 155 scenar at 2900fps.
    39°F, 29.35 inhg, 50% humidity. Wind variable from 4-6 o'clock at 2-6mph.

    Now I know you're going to say that 5° is a lot of cant, but it was done this way because I have a very controlled enviroment to shoot in at 600yds and didn't want to increase the range just so I could decrease the cant and my comfort. I would go further and say that I don't actually think 5° would be all that unlikely if someone was shooting in a position off of a sidehill (or you name it scenario) and didn't have any good references to find level.

    Click any image for full size:

    <span style="font-weight: bold">Set up:</span>


    <span style="font-weight: bold">Shooting:</span>


    <span style="font-weight: bold">Results:</span>


    Results:

    The top group aggregate measurement from centerline is 10.3" right (group measures 6-1/4")

    The middle group is right on centerline (group measures 2-7/8")

    The bottom group aggregate measurement from centerline is 8.1" left (group measures 4-7/8")

    Note: There is a small hole just low-left of the 5° right canted orange aim-point. This is a bullet fragment from the steel we were shooting after the test.
     
    #3
    Re: The effects of side to side cant - field test/pics

    Very nice job,

    The thing I find interesting in this is, the cant to the right, where the group size is 3X larger. If you consider all things being equal, as the saying goes, what would cause the group to not only go wider, but open up to 3X the level size ?

    Was it a compromise on the trigger use being right handed that leaning that way changed your trigger up enough to not only open things up but to move things farther ?

    Clearly on level your group is centered up so everything is dialed out in terms of other factors.

    Very nice, will be interesting to discuss
     
    #4
    Re: The effects of side to side cant - field test/pics

    I have never thought of doing this nice !
    I will have to do some tests like this now!

    thanks for posting.
     
    #6
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">The thing I find interesting in this is, the cant to the right, where the group size is 3X larger. If you consider all things being equal, as the saying goes, what would cause the group to not only go wider, but open up to 3X the level size ?

    Was it a compromise on the trigger use being right handed that leaning that way changed your trigger up enough to not only open things up but to move things farther ?</div></div>

    I don't mean to nitpick but it's really just over twice the size of the level group. It's definitely significant and I'd list the trigger control as a possibility, but I'm pretty anal about how I squeeze the trigger. Just as likely is the fact that it was the least comfortable position and my cheek weld wasn't as good with my head cocked up and over the edge of the stock. In order to be more consistent from shot to shot I should have found the angle and then tightened my bipod down. However, I wasn't looking to shoot great groups or see if the rifle cant played a roll in my group size or repeatability. I wanted to know if the rifle cant was a significant enough factor that I should be paying attention to the level on my rifle. In order to figure that out I just needed a decent cant and I needed to lob some down there in a manner that would give me significant enough data that I felt comfortable making a decision to continue using the level or not.

    I don't know that I'd take the data on group size and cant to heart without a couple more groups being shot. I wasn't really hogging down trying to shoot my best for this - just well enough to get a pass (the teachers loved me :))
     
    #7
    Re: The effects of side to side cant - field test/pics

    Funny; did anyone notice that the backer and target themselves were canted somewhat, and that the amount of horizontal displacement seems to differ in accordance with the direction of that cant? The stuff out rightward appears (to me) to be farther out than the stuff to the left, and the target frame's own cant seems somewhat toward the right as well.

    I had always believed I could work out cant by eyeball. Now I'm not so sure. Now I'm thinking that bad assumptions can be made regarding environmental references.

    This demonstation has made me a believer.

    Greg
     
    #8
    Re: The effects of side to side cant - field test/pics

    That's really <span style="font-weight: bold">nice</span> work.

    I certainly wouldn't worry about the group size - the <span style="font-weight: bold">worst</span> of those groups is still around an MOA - and the best is about a third of an MOA, which is really nice shooting at 600 yards!

    I put those parameters into JBM Ballistics, and it pretty accurately predicts the lateral offset you shot - it calculates the effect of a 5 degree cant with that load at 9 inches, which is about midway between the two measurements of group center.
     
    #9
    Re: The effects of side to side cant - field test/pics

    Excellent thread and very nice work. Not to detract from your thread but to piggy back on it. This is what chaps my butt when it comes to scope manufactures such as Leupold who have up to +/- 3 degrees of reticle cant (to be within their tolerances) when they ship a scope. A lot of seasoned and new shooters just don’t fully understand what a little cant can do at longer yardages. You proved what 5 degrees can do at 600. Take up to 3 degrees of cant from the scope manufacture; add that to a little human error and shoot at ranges beyond 400 yards or more. What you start to see, well hopefully you get the point.

    Please don’t start a scope manufacture bashing thread as this is not meant to detract from your excellent point.
     
    #10
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">Funny; did anyone notice that the backer and target themselves were canted somewhat, and that the amount of horizontal displacement seems to differ in accordance with the direction of that cant? The stuff out rightward appears (to me) to be farther out than the stuff to the left, and the target frame's own cant seems somewhat toward the right as well.

    I had always believed I could work out cant by eyeball. Now I'm not so sure. Now I'm thinking that bad assumptions can be made regarding environmental references.

    This demonstation has made me a believer.

    Greg</div></div>

    Greg,

    Great point and one that I hadn't noticed. I will say that I was very careful in leveling the target. I used an expensive 4' level that is tried and true. The targets have been through at least one complete high power season and they're going to be replaced this upcoming spring. They're warped enough that it's hard to actually get them into the frames. I wouldn't put too much faith in how the frame appears to be leaning. That being said - with the minimal amount of extra cant reflected to the right vs the left it is possible that somehow things got out of alignment slightly to the right, whether it didn't ride the rails up into position perfectly or whatever. Back up again and look at the center group and how it's pretty much dead nuts on the bullseye horizontally and you have an argument for it just being poor cheek alignment or trigger control given the positions I was shooting. What was it? Beats the hell out of me!
    smile.gif


    Now, having said that I do understand what you're saying about the frame leaning and using environmental references to find level perhaps being a flawed plan. Without a level to reference you might have assumed that the sides of the frame were plumb and used it to set your reticle. In this case you would have wound up dialing a little left as your shots grouped right. Something I've always done to find plumb is to reference several trees and use my gut instinct to tell me which are the most vertical. The horizon can be used sometimes, but not always. It's tricks of the trade to get your rifle level, and a bubble level or level grouse are just another tool we have access to. I use a USO bubble and I did notice an immediate increase in hits when I started using it. My own results vs what was commonly argued was what got me to conduct the test. If I didn't need the level I sure as hell wasn't going to keep it on my rifle - but I had suspected my instincts were correct and that I wasn't imagining things. I consider myself to be fairly scientific and if I'm wrong I'll gladly accept the correct argument and use it to better myself and my shooting.

    Lastly, another common argument I've heard lately is that the displacement left or right is due to the bullet drop. I'm of the opinion (though I haven't run the math yet and I'm not sure I will since I already know the results of a canted right = shot displacement) that it has to do with your line of sight vs bore and the height of your sight over your bore (or it could be bullet rise + bullet drop). I'd estimate that the further out of alignment they are the more you'll see that canting your rifle affects your point of impact. I'd be happy to be proven wrong, but don't think I will be (that's a challenge to you guys that believe otherwise, so I don't have to do the math). The results will be similar, but I think we're chasing our tail like the "universe revolves around the earth" model and would have to have some odd calculations to get the bullet drop model to predict our results vs a LOS/bore model. No idea if I'm right... don't want to do the math
    smile.gif


    Lindy found my results predictable based upon how JBM calculates it. Perhaps the author of JBM would chime in and let us know how he does so?
     
    #12
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: brasscow</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">The thing I find interesting in this is, the cant to the right, where the group size is 3X larger. If you consider all things being equal, as the saying goes, what would cause the group to not only go wider, but open up to 3X the level size ?

    Was it a compromise on the trigger use being right handed that leaning that way changed your trigger up enough to not only open things up but to move things farther ?</div></div>

    I don't mean to nitpick but it's really just over twice the size of the level group. It's definitely significant and I'd list the trigger control as a possibility, but I'm pretty anal about how I squeeze the trigger. Just as likely is the fact that it was the least comfortable position and my cheek weld wasn't as good with my head cocked up and over the edge of the stock. In order to be more consistent from shot to shot I should have found the angle and then tightened my bipod down. However, I wasn't looking to shoot great groups or see if the rifle cant played a roll in my group size or repeatability. I wanted to know if the rifle cant was a significant enough factor that I should be paying attention to the level on my rifle. In order to figure that out I just needed a decent cant and I needed to lob some down there in a manner that would give me significant enough data that I felt comfortable making a decision to continue using the level or not.

    I don't know that I'd take the data on group size and cant to heart without a couple more groups being shot. I wasn't really hogging down trying to shoot my best for this - just well enough to get a pass (the teachers loved me :))</div></div>

    If you were going to nit pick you'd have to acknowledge that you as a factor also increased the displacement downrange, in a way that is truly significant when looking at the big picture.

    I think you did an excellent job demonstrating this, but it also brings up other issues like the fact you were not comfortable when rolled over to your right, which increased the angular displacement as compared to the left. Not only in group size but in displacement distance... that is nit picking.

    So, the question would be, do you think on your right you had scope shadowing because your head was not getting the proper cheek weld. That is a question worth asking.

    If you're gonna explore this further, why not all the way.

    Again, huge props to doing to this, however why end the discussion on single segment when other factors are present in LR shooting.
     
    #13
    Re: The effects of side to side cant - field test/pics

    i'd imagine the group size can be atributed to the cheek weld and adressing the trigger, and how the rifle sets in the shoulder, along with the eye alignment issues. if shot from a rifle rest that was designed to be of a "barely touching the rifle" nature, i'm sure the groups would be more similiar

    but the test in itself proves the amount of how POI changes with the amount of cant, so it is a successful test of that.

    the rest of it can be addressed later, if need be, and for all the "numbers gurus" out there, if shot from a "barely touching the rifle" type a rest, some dope can be established to how far off center the POI would be per the amount of cant given.

    of course an ACD that's properly tuned mounted and "tuned" to a leveled rifle and optic reticle eliminates that need.

    nice post.
     
    #14
    Re: The effects of side to side cant - field test/pics

    oops just had a thought...

    many would expect the canted groups to be in the opposite direction with the line of sight / line of bore thing. in other words canting to the right - groups to the left and high, cant to the left - groups going high and right.

    i know it's been covered before on where the POI would be, i can't seem to locate the links to those threads, if someone has them, it would be nice to add them into the OP's post to compliment the OP's results.
     
    #15
    Re: The effects of side to side cant - field test/pics

    I think for some people using a level can be useful, however I have to question someone who is attempting to level off anything but the target and what they see in the scope.

    It never occurred to me to use the target frame to level the reticle on something like above. I would quarter the target and intersect 12 & 6 -- quartering the target properly is what helps you keep level, not the trees or target backer ? I don't use a horizon either, as I wouldn't be looking at the horizon, I am focusing on the target.

    it seems one who had difficultly leveling the reticle, especially after leveling the reticle to mount it, would have difficulty lining up iron sights. It's the same concept of centering the front sight inside the rear sight aperture. That is much more critical form of alignment and one where a leveling device can't help.

    But if you do find you have difficultly, then by all means use the level. But I would look at your technique for aiming in hopes of moving away from the dependency.

    For the tactical shooter, they are not always available, as well not always visible. On a slow fire square range if you can squeeze that last ounce of accuracy out, sure but then again, you do get sighters.
     
    #16
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">If you were going to nit pick you'd have to acknowledge that you as a factor also increased the displacement downrange, in a way that is truly significant when looking at the big picture.</div></div>

    Yes. I have no illusions about the group size not being directly attributed to how I shot the gun, not how the gun shot.

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I think you did an excellent job demonstrating this, but it also brings up other issues like the fact you were not comfortable when rolled over to your right, which increased the angular displacement as compared to the left. Not only in group size but in displacement distance... that is nit picking. </div></div>

    You're right, that is nitpicking. That group is 1/3rd MOA further from centerline than the left group and I would wager that my waning eyesight is largely responsible for my not being centered on the target as I pulled the trigger. I would attribute the group size to my not being comfortable. I decided about 45 days ago that when work slowed down a bit in the middle of December I'd get my eyes checked and get contacts. My eyes have been in a downward slide for years now and it's to the point that it is seriously affecting my ability to focus.

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">So, the question would be, do you think on your right you had scope shadowing because your head was not getting the proper cheek weld. That is a question worth asking.</div></div>

    I don't think that I had scope shadowing and I am certain my parallax was adjusted correctly. However, that doesn't mean that I didn't just pick an area slightly right of the bull as my center. NPOA would keep it there. These are mag loaded and shot without fucking around. 1, breath - 2, breath - 3, breathe and so forth. I keep a steady pace and maintain cheek weld, etc throughout the group.

    <div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If you're gonna explore this further, why not all the way.

    Again, huge props to doing to this, however why end the discussion on single segment when other factors are present in LR shooting. </div></div>

    I don't explore it all the way because that area of the subject doesn't interest me. I prefer to shoot and learn the more difficult skills like wind, coriolis, and spin drift (just fucking with you on those last two, Frank). I print groups sometimes to make sure I'm still doing things right, but I prefer to shoot steel at varying ranges from various positions. With only 15 rounds to collect our data I think this test could easily be read into too much. I shot left and right so that I could make sure it was consistently a certain distance from center, to validate the test for myself - and 1/3rd MOA is close enough for me.

    The areas you're looking in to are worth exploring, but I'm not the man for the job... I can only take so much of this boring shit
    smile.gif
    . The data collected from my test shouldn't be used to validate or refute any claims coming from anyone that does test that. This wasn't set up in a way that we could collect anything meaningful toward that end. That being said, your observations are correct and further testing may prove you right. I just can't say one way or the other because I didn't set out to collect that information. I would have been much more careful shooting my groups if I was - starting with locking the cant on my bipod in place.
     
    #17
    Re: The effects of side to side cant - field test/pics

    Nice report!

    Thanks for going to that much effort, and sharing your results.

    Your results look about like what i've seen from myself, shooting out of level, from uneven fp, to a target on uneven ground, with no visual references for plumb.

    I was about 10" left for a couple shots, then checked level and realized I was over a half bubble off, Leveled up, and was right on the money. That was shooting Broz's rifle. I put levels on my rigs the next week.

     
    #18
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">I think for some people using a level can be useful, however I have to question someone who is attempting to level off anything but the target and what they see in the scope.

    It never occurred to me to use the target frame to level the reticle on something like above. I would quarter the target and intersect 12 & 6 -- quartering the target properly is what helps you keep level, not the trees or target backer ? I don't use a horizon either, as I wouldn't be looking at the horizon, I am focusing on the target.</div></div>

    All just tricks of the trade... they all work in different situations. I don't see how quartering the target and intersecting 12 and 6 would lead to a result different than just using the side of the target as a plumb line. Either way you'd wind up out of level by how much the target is leaning. Not contesting it being the right way, as you'd never be off target - only that the end result would be the same when looking at shot displacement?

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">it seems one who had difficultly leveling the reticle, especially after leveling the reticle to mount it, would have difficulty lining up iron sights. It's the same concept of centering the front sight inside the rear sight aperture. That is much more critical form of alignment and one where a leveling device can't help.

    But if you do find you have difficultly, then by all means use the level. But I would look at your technique for aiming in hopes of moving away from the dependency.

    For the tactical shooter, they are not always available, as well not always visible. On a slow fire square range if you can squeeze that last ounce of accuracy out, sure but then again, you do get sighters. </div></div>

    They're not always available... that's why its important to have other tricks in our bag. The level is just one of them. They aren't just useful on a slow fire square range. They're useful in tactical comps where an extra few seconds usually doesn't hurt anything. They're useful for LE and military if they have time to set up the shot. They're useful because as this whole thing demonstrates, that extra two seconds to consult your level can be the difference between a hit and a miss and you can't always afford a miss. How much extra time does that miss cost you? How many points in a tactical comp? Worth the extra time? Yes and no... if I have the extra time and my level is functioning and visible then I'll use it. If not, I'll use the other skills I've developed and my crafty brain to figure out how to do it. It's merely a tool, and one that doesn't detract from my shooting or add noticeable weight to my kit.
     
    #19
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">
    If you're gonna explore this further, why not all the way.
    </div></div>

    ...cause you didn't send him enough ammo to did it with
    laugh.gif
     
    #23
    Re: The effects of side to side cant - field test/pics

    Guys, I'm glad the info is so well received!

    I just printed the target to PDF so anyone can use that to do their own test. You can either print it yourself on a plotter or I think kinkos will do it as well. In a worst case you could tile it onto multiple pages (an option during printing) and then tape them together.

    target here

    No idea why it has little dash marks through it and what-not, it's just the way it converted to pdf.

    It wouldn't be much for me to change this and post another, so if someone is honestly going to do their own test but wants the cant 2° or whatever - let me know. But... if I send it you have to post the results.

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sean the Nailer</div><div class="ubbcode-body">The beginning of a very interesting tangent. </div></div>

    Yeah, Frank and Greg brought up some interesting ideas. Even if they don't get tested it's something to think about - Are we giving every shot our all? Are we fucking up the fundamentals just because we're being lazy or not in a position we like to shoot from? What other methods can we use to field level our rifle?
     
    #25
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ~Ace~</div><div class="ubbcode-body">Great Post !

    <span style="font-style: italic">It looks like the Spin Drift was Exaggerated bu the Right hand Cant !
    smile.gif
    </span> </div></div>

    Wait, that wasn't coriolis effect?
     
    #26
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JFComfort</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ~Ace~</div><div class="ubbcode-body">Great Post !

    <span style="font-style: italic">It looks like the Spin Drift was Exaggerated bu the Right hand Cant !
    smile.gif
    </span> </div></div>

    Wait, that wasn't coriolis effect? </div></div>

    lmao, thats exactly what I was thinking, you beat me to it Joe!
     
    #32
    Re: The effects of side to side cant - field test/pics

    Thanks for doing this test and sharing the results.

    I'm a HUGE advocate of using levels for long range shooting. If you're shooting past 300 yards a level is indispensable.

    It's always gratifying to see when a ballistics model prediction matches what happened in a field test. I consider the prediction of 9" to *match* the result of 10.3R and 8.1L. Why it was more in one direction than the other, and why the groups were bigger are good questions, but I'd like to focus on the ballistics for now.

    The models (JBM) prediction was accurate at 600 yards, so we should be confident it's solving the problem correctly and will provide accurate predictions at other ranges as well. JBM predicts around 30" of horizontal displacement for a similar trajectory with 5 degrees cant at 1000 yards, which is a far more dramatic displacement than the 9" at 600. Granted you're unlikely to have 5 degrees of cant in any scenario where you're trying for zero, but is it possible to have 2.5 degrees of cant with the unaided eye? That corresponds to a 15" miss.

    With the use of a level, I estimate you can resolve within +/- 0.5 degrees pretty easily, which narrows your 'cant' miss distance down to less than 3" at 1000 yards, regardless of the terrain, or if you have any good vertical or horizontal reference lines in your FOV. Why not use the aid? It's not heavy or intrusive. You can ignore it on close shots where it's not as critical.

    For those who were interested about the math of determining cant, it's pretty easy. You essentially take the total drop at the range of interest, and multiply by the sin of the cant angle. For example, if the total drop from the bore line is 300" (typical 1000 yard drop), and you have a 5 degree cant, the horizontal displacement will be 300*sin(5) = 26". If the cant angle is 1 degree, the displacement is 300*sin(1) = 5". This leads to a rule of thumb: for every 1 degree of cant, you suffer about 5" of horizontal displacement at 1000 yards (more or less depending on how flat the trajectory is).

    It's pretty easy to visualize where the error comes from if you take it to the extreme. For example, if you shot with a 45 degree cant, and you had 30 MOA of elevation dialed on, then you can expect that a great deal of that 30 MOA of sight adjustment will be horizontal. If the scope is canted 90 degrees (laying on it's side), then all 30 MOA is horizontal. The case of a slight cant is the same effect, but to such a small degree that it's harder to visualize. When you have 30 MOA dialed on, and the scope is tilted slightly to the size, a small component of that 30 MOA 'bleeds into' the horizontal plane.

    Imagine if you were using a reticle hold over, and there was a big cant. Using a reticle hold-over by putting a mil-dot (or some other reticle feature) directly on the target, the actual cross-hair is not directly above the target. The bullet will fall from the center of the cross-hair (because that's how gravity works) and will strike below the cross-hair where, in the case of excessive cant, the target <span style="font-style: italic">isn't</span>.

    Once again brasscow, thanks for the effort.

    -Bryan
     
    #33
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: JFComfort</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ~Ace~</div><div class="ubbcode-body">Great Post !

    <span style="font-style: italic">It looks like the Spin Drift was Exaggerated bu the Right hand Cant !
    smile.gif
    </span> </div></div>

    Wait, that wasn't coriolis effect? </div></div>

    Just Drink your SpinD and don't worry about it . . . . .
     
    #34
    Re: The effects of side to side cant - field test/pics

    First, thanks again for a great post.

    One thing Io am curious about is that I would expect the canted groups to be lower on the target since part of the dialed elevation was "converted" in effect to windage instead. In other words, part of the elevation dialed was negated by the cant.

    Why weren't the canted groups noticeably lower? I havent done the math but I know you are loosing some elevation and that ought to show.

    Anyone? Buehler?
     
    #35
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KYpatriot</div><div class="ubbcode-body">First, thanks again for a great post.

    One thing Io am curious about is that I would expect the canted groups to be lower on the target since part of the dialed elevation was "converted" in effect to windage instead. In other words, part of the elevation dialed was negated by the cant.

    Why were the canted groups noticeably lower? I havent done the math but I know you are loosing some elevation and that ought to show.

    Anyone? Buehler?</div></div>

    They should be .4" lower. Not really even measurable given the small sample and other variables involved.
     
    #36
    Re: The effects of side to side cant - field test/pics

    Ok, my bad, not having done the math I didnt realize the amount would be lost in the noise, just knew it should be there. Thanks for making up for my laziness, I'll try not to let it happen again!
     
    #39
    Re: The effects of side to side cant - field test/pics

    Would be interesting to have him on a board and then tilt the board the 5 degrees left and right and see if that takes the human error out of the equation. Maybe a brick left side then right side.
     
    #40
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ranger1183</div><div class="ubbcode-body">Since we're on the topic, what is the preferred leveling mechanism. A folding or a fixed level or something else entirely? </div></div>

    There's a few different styles. I've seen base mounted, tube mounted, ring top mounted.

    I went with a tube mounted design with the bubble riding centerline (some are extended out to the side). Upside is it is fairly protected, and unobtrusive. Downside is it's not as convenient to check, you have to raise your head slightly to check it.

    CopyofPB140003.jpg
     
    #41
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sunnyside Scott</div><div class="ubbcode-body">Here is a Demo from my air rifle days, most FT competetors will use a anti Cant device. Lobbing projectile down range is the same big or small.
    SScott
    http://www.arld1.com/targetplottrajectory3.html </div></div>
    Now THAT page is outfriggin'standing.

    Those ISU (I'm old, now it's UIT???) targets are quite demanding. My smallbore standing cant was about 15 degrees, and even though we shot at 50 feet on the gallery course, that shows the amount right I had to correct. I eventually went to the same cant in all three positions, plus sitting when we shot NRA, and just added a click of the *other* for every four or five clicks of change.

    Was glad we didn't change ammo and zeros that often.

    Living without sighters--it's a different world.
     
    #43
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Grump</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sunnyside Scott</div><div class="ubbcode-body">Here is a Demo from my air rifle days, most FT competetors will use a anti Cant device. Lobbing projectile down range is the same big or small.
    SScott
    http://www.arld1.com/targetplottrajectory3.html </div></div>
    Now THAT page is outfriggin'standing.</div></div>

    I'll second that! Great visualization of how cant affects trajectory.
     
    #45
    Re: The effects of side to side cant - field test/pics

    I'm puzzled and most be doing something wrong in JBM. With zero wind, I of course get 0.0 drift @ 1000 yards and a 370" drop. Using the formula Bryan presented above, I end up with sin(5 deg) * 370 = 32.24". But when I enter 5 deg in the cant field in JBM, I get a drift of 3.7":

    cant_angle.PNG
     
    #46
    Re: The effects of side to side cant - field test/pics

    It's because your zero is set at 100 yards.

    Set your zero range for 1000 yards and you'll see much more horizontal deflection.

    This can be tricky.

    Remember the effect of cant comes from the fact that a portion of your <span style="font-style: italic">dialed</span> elevation is converted to 'windage'. If you have a 100 yard zero, there is very little elevation dialed, so the effect of cant is minimal.

    However if you're elevation zero is set at 1000 yards, there's lots of elevation dialed on, and a slight tilt will put quite a bit of error in the windage plane.

    -Bryan
     
    #47
    Re: The effects of side to side cant - field test/pics

    Thanks Bryan. I wouldn't have thought of that. But, help a math-n-logic challenged guy here: If I have a cant, e.g. 5 deg. and dial in the 10.3 mils to get on target @ 1000 yards then isn't that where I'd be inducing that hefty error? So why doesn't JBM tell me, in effect, "If you dial in this amount of elevation and don't straighten out your rifle, son, you're going to hit 36" right." even with the 100-yard zero? Isn't it assumed that the shooter will dial in the recommended amount of correction?
     
    #48
    Re: The effects of side to side cant - field test/pics

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azimutha</div><div class="ubbcode-body">Isn't it assumed that the shooter will dial in the recommended amount of correction? </div></div>

    It assumes you dial the elevation for the zero range that you input. Remember the ballistics program is just running a trajectory based on the inputs you give it. If you tell it you're zeroed at 100 yards, the horizontal displacement from cant will correspond to the elevation required to zero at 100 yards.

    If you want to see the consequence of cant for a trajectory that's zeroed for 1000 yards, you have to tell the program that.

    I realize this is confusing. I did a double take the first time I used JBM to look at cant and it took a while to sink in. In the end, the program was right and it was my lack of understanding that made it look 'off'. Brad is a sharp guy, and as many eyes that have been on his programs, I doubt there are any major or minor errors left.

    -Bryan
     
    #49
    Re: The effects of side to side cant - field test/pics

    WHOA! I had no idea that Leupold had that much of a tolerance for reticle cant. I wonder what NF scopes consider acceptable to pass their QA standards?

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Jeff in TX</div><div class="ubbcode-body">Excellent thread and very nice work. Not to detract from your thread but to piggy back on it. This is what chaps my butt when it comes to scope manufactures such as Leupold who have up to +/- 3 degrees of reticle cant (to be within their tolerances) when they ship a scope. A lot of seasoned and new shooters just don’t fully understand what a little cant can do at longer yardages. You proved what 5 degrees can do at 600. Take up to 3 degrees of cant from the scope manufacture; add that to a little human error and shoot at ranges beyond 400 yards or more. What you start to see, well hopefully you get the point.

    Please don’t start a scope manufacture bashing thread as this is not meant to detract from your excellent point.
    </div></div>
     
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