If you were to ask a group of rifle-scope fanatics, what are the most important features of a perfect rifle scope, you would probably get a few different answers. Among them though, you would for sure hear things like; optical quality, repeatability, and of course accurate tracking. This may come as a surprise to some, but many times the values you see on the turrets of your beloved riflescope are more like a suggestion than an accurate measuring tool.
Tracking
Tracking is one way to describe the movement of the erector inside a riflescope. When you adjust the elevation or windage turret, the erector than encases the reticle moves on either or both axes. The consistency and quality of the erector construction greatly effect the way it moves, and like nearly everything in the precision rifle game, consistency is what allows us to shoot accurately.
There are several ways a scope can track poorly, but they all result in inconsistent movement of the reticle. Erectors usually have a spring tensioner opposite the two turrets, its job is to push back against the elevation and windage turrets. but if it fails to do it job, you will see problems. Your reticle can be out of place in a variety of ways, if the spring is weakened, the reticle can be impaired in its movement. This could result in jumping after adjustment, some may remember the old practice of tapping on the scope after adjusting the turret, which was to avoid this very issue. Luckily for us today, scopes have improved greatly, and unless your buying some fifty-dollar 要沐考 scope you probably don’t need to worry about it.
Another problem that typically follows low budget scopes is a varying change in values across the turrets travel. A good quality MRAD scope will move the reticle one MRAD for every ten clicks the turret is turned. Some scopes are not exact, but they are at least consistent. For example, instead of moving the reticle one MRAD for ten clicks, it might move the reticle .982 MRAD for ten clicks. While this is less than perfect, it is much better than the worst option, which I’ll explain shortly.
A good scope will move one MRAD per ten clicks on the very first MRAD of rotation, and it will also move one MRAD per ten clicks on the last rotation whether that be two MRAD later or twenty. Even the less desirable scope that doesn’t quite move the whole MRAD, but .982 MRAD hopefully maintains it’s .982 MRAD at both extremes of the turret travel. The worst option I mentioned above is a scope that cant make up its mind; one that moves one MRAD for the first ten clicks, and then maybe .982 for the second ten clicks, and then some other basturd amount as it continues its travel. This may be caused by bad springs, poorly machined turrets, or other issues inside the scope.
In addition to inconsistent movement, there is also reticle cant to watch for. Reticle cant is just what it sounds like, the reticle is not perfectly vertical and horizontal inside the scope. We level our scopes properly to avoid this very issue; if we crank elevation into the turret with the scope not perfectly leveled, the center of the reticle begins to wander left or right to the acute side of your unlevel mounting job. And the further up you dial, the farther out its going to get.
External leveling issues can at least be corrected once discovered, but if your reticle is canted inside the scope you are probably going to be sending it in for repair as it’s not serviceable unless you are exceptionally brave or stupid. A perpendicular reticle can be cross-checked using the old plumb-bob method, hanging a weight from a string that is hung in front of the leveled rifle to ensure the reticle matches the straight line pulled taught by gravity. Often times the reticle cant is induced by rotation caused using the power ring. You can see a change in the reticle angle when adjusting the magnification power.
So Let’s Test Already!
Hopefully your not completely terrified that your scope is garbage now after all these possible issues. So let’s get down to finding out if your scope is perfect or flawed, or perhaps more accurately just how flawed it is. Because even the best scopes can be off a little bit, more often than not it isn’t enough for even the best shooters to notice.
The very first and most important thing you can do is to find an EXTREMELY solid place to mount your scope. Like literally nothing is too robust for what we are going to do, seriously if I could put a picatinny rail on top of a Caterpillar D10 I would use it. The reason we want such a solid mount is because we will be cranking it significantly and repeatedly, and if the scope itself moves AT ALL during the process your results will be skewed.
Since I haven’t found a pic-railed D10, I have instead taken other suitable options. The easiest I have found is to use a strong C-clamp to firmly hold my scope down to a table or countertop. I usually use shims to level the scope, and pieces of paper to protect from marring my scope or rings.
The trick is to mount your scope as solid as possible, and aiming at a suitable target that ideally is exactly one hundred yards away. I say exactly because I am mathematically challenged. If your target is exactly (and I mean exact) one-hundred yards away, you wont have to do the math equations necessary that I’ll explain later. For now we will assume you have a hundred yard target you walked out with a tape. And on/at that target distance you should hang a precise yard-stick or even better something longer like a surveyors ruler. Once you have everything assembled, ensure both scope and ruler are level and perpendicular.
The Test
With your scope firmly mounted and sighted in on the hundred yard measuring stick of your choice, you can start the test. From a marked point on the ruler, you should be able to measure out the MIL’s on your reticle. The first MIL up/down should be 3.6 inches or 3 and 3/5 from your crosshair, and if you dial one MRAD (ten clicks) up, your crosshair should now be on that same 3.6 inch mark. You can do this across the span of the entire elevation turret, if you dial ten MRAD (one-hundred clicks) you should have gone from zero to thirty-six inches. The test can obviously be done in the same way for MOA as well, but its gayer.
You can also get really extreme and setup the ruler on the horizontal axis and check your windage turret as well if you really feel thorough. But it is very important to do the process several times, taking the turret all the way up and down, ensuring that the movement is consistent and uniform. The math I spoke of above is used to determine how close to correct your scope is, I’ll do an example for you: If you turn the turret ten MRAD up (one-hundred clicks) it should have moved the cross hair thirty-six inches at one-hundred yards. If it didn’t, use your math’s to see the actual value. If one-hundred clicks moved it thirty-five and one-half inches, you can divide 35.5 by 100 and get .355, which is %98.8 of .36, that means when you dial ten clicks up you are actually getting 98.8% of your one-MRAD instead of the full 100%. Now, if your shooting a 300 Winchester at deer inside five-hundred yards that is barely enough to matter. But if you are a competition shooter or someone that frequently shoots long-range this is a good thing to know if only to correct your elevation units. That is one of the very useful tools I find in modern ballistic computing apps, the ability to correct the value of your turret clicks.
More important than whether or not your scope tracks perfectly, is to know the actual value that it does move. Even if your scope is off by 10% you can deal with it as long as you know, and it is consistent. That said I wouldn’t be paying for any scope that far off.
On the off chance you don’t have the exact one hundred yards, you can once again use your math skills to divide your results by whatever the distance you do have to check the turret travel.
While you have your scope locked up tight, it would be a good time to see if there is any reticle cant both when you adjust the magnification or turrets. If you do find some disparity in the cant, I would recommend you replace or repair it since this isn’t one you can just live with.
Conclusion
I hope this has been helpful for you, and if you find your scope to be sub-standard consider it a favor I did you. Better to know than to always wonder why everything is just a little bit off. Rifle scopes are fascinating tools, and knowing more about how they work can only improve your use of them. Check out your scopes and see how they measure up to each other.
-CBM