Preface
You may have heard of using canted scope mounts, and if you are unfamiliar why or perhaps trying to decide if you need one. Today we are going to discuss the subject. You might ask why use canted scope mounts and how much you might need? It is particularly important for long range shooting applications. To put it simply, a canted scope mounting system is designed to allow better use of a riflescope’s internal travel. Hopefully by the the time you’ve finished reading this, you’ll understand what if any size canted scope mounting system best fits your needs.
A Riflescope’s Internal Travel
To start out, we need to understand how a scope works. Inside a rifle scope you will find the reticle, which is mounted on a movable structure called an erector tube assembly. Moving the reticle up and down and left to right is done using covered or exposed turrets. These turrets move the recticle within the tube of the scope allowing you to align the reticle with the point of impact of the gun. This is what we do when we “zero” a riflescope.
All scopes have limits in their internal travel, and the bigger the scope tube is the more travel they can accomodate. Thirty years ago, most scopes used a smaller one-inch tube. Mainly because it allowed enough internal movement to allow zeroing most rifles. As technology advanced, and shooting distances quickly extended, it became more common to use a bigger tube to allow for additional movement.
Why More Movement?
Even novice shooters understand that the farther away something gets, you have to aim higher to hit it. Compensating for the drop of a bullet during flight can be done by holding high or by offsetting the sight. When you dial the turret of a riflescope down, it forces you to hold the rifle higher in order to put the crosshair on the target.
Ballistic prediction allows us to calculate how much we need to correct for. Which can then be input to the scope using the turret to adjust the offset a specific distance.
As we continue to push the boundaries of long-range shooting people want more and more ability to push their equipment. But every scope has its limits, you can only dial the scope so far before the reticle bottoms out. At that point you’ll be forced to hold over the target if you want to shoot farther.
MOA vs. MRAD
Rifle scopes typically use one of two measuring scales, one is the minute of angle or MOA measurement. The other is called the milradian scale or MRAD for short. And if you are super high speed it can be further shortened to MIL.
Both of these scales serve the same purpose, and are simply different methods of measurement. It isn’t actually, but is often compared to the difference between inches and centimeters. They are two different scales to measure the same thing. Most rifle scopes come in one or the other gradations and sometimes offer different models for each.
These numbers are important not because I am a math nerd. When you hear the term weaponized math its because these numbers are particularly helpful when killing a target. I would recommend you study further to better understand MOA and MRAD as it will only help you be smarter about the subject.
Your Scope’s Internals
The amount of movement your reticle can move within the scope is measured by you guessed it; MOA or MRAD. Lets say your scope has an internal movement of 15 MRAD in elevation (up & down), and 10 MRAD windage (left & right). That means that no more than 15 MRAD can be adjusted within the scope, but that is before you’ve even zeroed the rifle. So AFTER you zero the scope to the rifle you may have even less reticle movement.
This is why scope tubes keep getting bigger, because a 30mm tube has more room for travel than a one-inch tube etc. But lets say you zero your rifle, and in the process you use four of the available 15 vertical MRAD. That means you’ll only have 11 MRAD of vertical travel left.
You can see then why having a 34mm tube with something like 32 MRAD of vertical travel would be advantageous to a long-range shooter. Stay with me here, because if you had 32 MRAD of travel and used four to zero the rifle, 28 is more than the 11 you had with the other scope. Does that make sense?
Canted Scope Mounts
Canted scope mounts are typically either a canted scope base rail, or a scope ring set with a cant built-in to the mount. Both options accomplish the same purpose, they offset the scope a specific amount. These canted scope mounts are typically sold in various degrees of cant, usually 20, 30, 40 or more MOA, which can also be delineated in MRAD sometimes. Especially if you find yourself in Europe.
The reason they are made with varying degrees of cant is so you can optimize for your purpose. For example, lets say you want to maximize the distance of your 6.5 Creedmoor (because thats what Creedmoor people do). And the furthest you can shoot is 1300 yards with the scope turned all the way to maximum elevation. But using our example from before, lets say you used four MRAD in order to zero the rifle. (what that means is you have 4 MRAD you can still dial down when the scope is at the rifle’s zero). That means you have 4 unused MRAD of travel, that could be used if you offset the scope 4 MRAD down.
Canted scope mounting systems allow you to setup your riflescope as close to the mechanical bottom of its internal movement as possible. This allows you to get the maximum adjustment possible out of your given scope.
Note: It’s probably never a good idea to run a scope all the way to the bottom or all the way to the top of its travel. Better to stay at least several clicks away from the extremes.
The amount of mechanical adjustment directly affects the distance envelope you can engage on your rifle and scope combination. Below you can see how two identical rifles have differing trajectory envelopes based on canting the scope on the second rifle. Both rifles still have the same available amount of scope travel, but one is able to maximize it with the scope cant.
Extreme Long-Range
Canting the scope in the extreme is sometimes done when shooting extreme long-range, with amounts like 60, 80, 100 or more MOA of scope cant. Most of those rifles never shoot close distances, and I’ll tell you why that’s a good thing.
When you cant the scope, it pushes the envelope of your scope adjustment out. But it also might push your ability to zero out further too. A typical 20-30 MOA scope cant won’t be an issue most of the time. But it could require you to zero your rifle at 200 yards or more if you get real aggressive. Moving the envelope of your scope further out, can have the same effect on your zero distance. So instead of having a range of 100 to 1300 yards, you might have a range of 300 to 1600 yards. Just something to stew on while you consider your options.
Final Thoughts
I hope this has all made sense to you. Finding the right scope mounting solution is paramount for long-range shooting, I hope it is clearer to you now as to what you might need. Sometimes it takes a little trial and error to find out the best option, but once you get the right setup you’ll be glad you went through it. And in the process you’ll probably learn a few things about mounting scopes and how to adjust them.