dscottdennison

March 9, 2012, 09:33 AM

I recently purchased a new long range scope, and while I was shopping around online I came across some incorrect information regarding reticle perpendicularity. Many people were experiencing slightly canted reticles (in relation to turrets) and were frightened that this would somehow put them 3 feet or more off target at the coveted range of 1000 yards!

So, I just wanted to do a little math and clear things up.

First, let me just say that it is not all that difficult to notice as little as a 1 degree variation in angle by eye at the reticle. Some people were stating as much as 5 degrees of variance between reticle and turret! That's an extreme case, and most were talking well under that, so I will use 2.5 degrees for my calculations. It seems that canted reticles are not all that uncommon, but I will show you that it is nothing to worry about. All of this also holds true if the reticle and turret are aligned but the scope is installed slightly tilted one way or the other. So, those scope leveling systems are just another bit of marketing BS in the gun world...

Imagine a right triangle in the same plane as your reticle while looking through the scope, pointing downward. If you align the reticle squarely, and your turret is angled 2.5 degrees off to the right, the bottom angle of your triangle is obviously 2.5 degrees. For this example, I will use MOA measurements. At 100 yards, 1 MOA is about 1.047 inches. We will figure out how many inches of horizontal variance result per click of a 1/4 MOA per click scope with a turret that is offset by 2.5 degrees from the reticle.

1/4 x 1.047 = 0.26175" This is the hypotenuse of your triangle, since this is how much each click of the turret raises the reticle, but the turret is offset, not the reticle. Now we have the simple equation: sin(2.5 degrees) = x/0.26175, where x = the horizontal leg of your triangle. This X value is how much horizontal variance will result for each click of your scope. Doing the math, we find that X = about 0.0114. So, just making up a number of 30 MOA of correction needed to get a large caliber rifle to 1000 yards while zeroed at 100 yards, this comes to about 1.37 inches of horizontal variance.

In simple terms, if you zeroed your rifle at 100 yards, drew a perfectly vertical line through the bullseye, cranked up 30 MOA and fired another group while aiming at the same bullseye, the group would be less than 1.5 inches off to the right of the vertical line.

Therefore, the only people who need to worry about a few degrees of cant between reticle and turret (which is evidently pretty common) are those who are worried about 1.5 inches at 1000 yards...

So, I just wanted to do a little math and clear things up.

First, let me just say that it is not all that difficult to notice as little as a 1 degree variation in angle by eye at the reticle. Some people were stating as much as 5 degrees of variance between reticle and turret! That's an extreme case, and most were talking well under that, so I will use 2.5 degrees for my calculations. It seems that canted reticles are not all that uncommon, but I will show you that it is nothing to worry about. All of this also holds true if the reticle and turret are aligned but the scope is installed slightly tilted one way or the other. So, those scope leveling systems are just another bit of marketing BS in the gun world...

Imagine a right triangle in the same plane as your reticle while looking through the scope, pointing downward. If you align the reticle squarely, and your turret is angled 2.5 degrees off to the right, the bottom angle of your triangle is obviously 2.5 degrees. For this example, I will use MOA measurements. At 100 yards, 1 MOA is about 1.047 inches. We will figure out how many inches of horizontal variance result per click of a 1/4 MOA per click scope with a turret that is offset by 2.5 degrees from the reticle.

1/4 x 1.047 = 0.26175" This is the hypotenuse of your triangle, since this is how much each click of the turret raises the reticle, but the turret is offset, not the reticle. Now we have the simple equation: sin(2.5 degrees) = x/0.26175, where x = the horizontal leg of your triangle. This X value is how much horizontal variance will result for each click of your scope. Doing the math, we find that X = about 0.0114. So, just making up a number of 30 MOA of correction needed to get a large caliber rifle to 1000 yards while zeroed at 100 yards, this comes to about 1.37 inches of horizontal variance.

In simple terms, if you zeroed your rifle at 100 yards, drew a perfectly vertical line through the bullseye, cranked up 30 MOA and fired another group while aiming at the same bullseye, the group would be less than 1.5 inches off to the right of the vertical line.

Therefore, the only people who need to worry about a few degrees of cant between reticle and turret (which is evidently pretty common) are those who are worried about 1.5 inches at 1000 yards...