Below are some pictures of a bit of shooting today. I still have a larger view of the right side that I'm trying to get to post but I think all areas can be seen. All canted shooting was done with counterclockwise rotation-bore moving right in relation to LOS so cant error was causing movement to left of POI. Note that wind was from the left and was gradually increasing which will be noted below.
Left photo (and center because I couldn't get the right photo to load) shows zeroing open sights at 20 yards then canted shots (using the dashed line as cant amount) at 40 yards. Very hard to shoot that way as most can imagine but you can see the displacement. I believe I'm pretty accurate with the mark for center at 1" left. A gust of wind caught the one shot with the (X wind) marked by it. These LGV open sights are relatively tall and that increases the amount of cant error (or said another way, it decreases the difference that would be seen between the open sights and the scope) than would more common lower mounted open sights. All relative
Right photo shows both the open sights and the scope. Two marked groups can be seen on the scoped side, one circled and one in squares. They correspond to the two lines for cant marked. More cant, more movement of POI to left. The more relevant point is that the displacement to left with open sights (lower) seems to be about 1" while the displacement to left with the scope (higher) is noticeably more, as marked below the groups.
Not as precise as it could be and I will attempt to do similar at some point using two scopes but I do believe it illustrates the point. Also, the wind from the left was gradually increasing throughout the session so the open sight shooting done first would have been less impacted by the wind from the left than would the scoped shooting that was done second. The scope was mounted in high rings on top of a dovetail to picatinny adapter for as much height as I could get. The open sight height on the LGV is about 1.25" (relatively tall for open sights) and the mounted scope height was about 3".
I believe this shows that the higher the sight is mounted, the more cant error will be seen in POI.
Some things I'll note for the naysayers.
First, I made sure to try to cant the open sighted shooting AT LEAST to the line marked as much as possible and that should mean maximum displacement of POI to the left. Similarly, I tried to only get close to the cant marks with the scope thus canting relatively less thus minimizing displacement. In other words, I tried to minimize any "fudging" to increase the low sight displacment seen and decrease high sight displacement seen. And still, even along with the increasing wind from the left that came up while shooting with the higher sight which would decrease the amount of displacement seen, the higher sight created MORE displacement to the left than did the lower sight. Higher sight, more cant error.
Second, and before someone chimes in with "it's a ranging error", I'll state clearly that after zeroing at 20 yards I fired shots with each sight at 40 yards to determine amount of drop for each and hold accordingly. The tall open sights on the LGV created a POI just at the top edge of the aim point at 40 yards so range was correct with that aim. For the tall mounted scope, the shots were hitting 1/2 dot high at 40 yards so I used a 1/2 dot low hold as the aiming point and verified both correct for the range with sighter shots. NO RANGING ERROR. Each elevation was verified correct for the distance.
Third, note that this comparison distance is only 1 multiple of the zero distance. Longer distance equals not only more displacement of POI for each sight height but also increases any difference between the two because of trigonometry-it is dependent on the angle created by the cant.
I hope to be able to do this under more controlled conditions (indoor or at least under completely calm conditions) and with laser sighting (to make the shooting more precise) at some point and I intend to try to get that done but all of this involves removing scopes, stacking mounts, rezeroing, and trying to get the shooting done so it is time consuming. But I believe the pictured results show that higher sights create more cant error effect on POI.
