I am relatively new to distance shooting and have noticed that I repeatedly shoot to the right at distance...the greater the distance the farther to the right I shoot.
I suspected it could be the result of rifle cant so today I decided to experiment with the impact rifle cant has on bullet impact. I had been shooting 77g SMK but used 69g SMK for this test.
The 69ger's shoot high at 300 yds compared to the 77's. My hold was on the 3rd mil-dot under the crosshairs. The top two holes are the initial "straight up" shots using the 3rd mil-dot. The two to the left were shot with the rifle canted at approximately the 10:00 position (scope left of the bore). The two holes to the right were fired with the rifle canted at approximately the 2:00 position (scope right of the bore). Notice that the holes are directly under the center of the crosshairs and low of the center. I suspect that the greater the distance, the greater the difference would be.


Results: While using mil-dots below the crosshairs cant to the left - shoot low and left; cant to the right - shoot low and right. I suspect that the farther the dots are from center, the more pronounced the deviation. I realize this was a limited test, but the results are pretty interesting - to me at least.

Your shots being lower were probably because of using the mil dots.  As in the center of the crosshair was rolled more to the right or left and down, if that makes any sense.

I know very little about long range ballistics, but perhaps gyroscopic precession has some affect on the shots.

http://www.riflescopelevel.com/cant_errors.html

Cool, bookmarked for further reading.



 

I may not be perfectly understanding what you are asking, but I think I do, so...

Think about how we are able to lob a round into the target at 300 yards.  We physically drop the breech end of the barrel down by raising the sights.  The bullet travels up, or climbs, as it leaves the barrel, because we lower the rear / raise the front of the barrel (by adjusting either the front or rear sight––or the scope) in relation to our line of sight looking (which is always a straight line).  Now turn the gun over on to its right side and look through the sights.  Which way is the barrel pointed now?  It is actually pointed or aimed to the right––because the sights still work the same way, you are just using them to affect a change in a different plane.  Now since it's laying on its side, perfectly flat, you are no longer compensating for the drop of the bullet (with the sights), so the round will impact lower on your target, but it will also impact to the right.  Lay the gun all the way over on its left side, and the barrel is now physically pointing to the left.  Now you will get a group to the left and a little low.  The less cant, and the shorter the distance, the less dramatic the results will be.

Every time a teach a patrol rifle class to some new officers I shoot a demo of a canted rifle, just so they can see the effect on POI.  Now for most people, with a duty AR, iron sights (or a RDS), shooting from an unstable position such as roll-over prone, the holes at 100 yards are more of a pattern than a group, but sometimes it's evident.

And if you already knew all that, or this wasn't what you were asking about––sorry I wasted your time