When a 10th isn’t a 10th

When a 10th isn’t a 10th

Almost everything we do with a precision rifle involves a rifle-scope, whether it is target identification or adjusting for come ups and such. We have become so dependent on them that the idea of using iron sights on a precision rifle seems almost foreign or backwards.  Not that there’s anything wrong with that, but I spend a good portion of my time peering through scopes. But how many of us have stopped to think about that expensive miniature telescope we so carefully mounted to the top of our rifle?

Most of you are probably quite aware of the proper way to mount a scope, we take extreme care to ensure the scope is perfectly level, and properly torqued and such. But I’ll bet just as many of you have never done thorough testing of your scope to see if it does what it says it does. I hope you’re not scratching your head wondering what it is I’m talking about, but just in case you are, I’ll explain.

Riflescopes are mechanical, and like everything mechanical they can break or fail, or they can come flawed from the factory. It’s pretty easy to tell when your scope is broken or otherwise not working, but it is a much harder thing indeed to find out if it came slightly flawed from the factory. It’s harder still to see if the flaw is a deal-breaker, or if it is something you can live with. Let’s start by discussing a few common things that you might experience.

Reticle Cant

Reticle cant is when the reticle inside your scope isn’t completely level, or even worse, it varies depending on other things. For example, your reticle might just be out of plumb, or it could be mobile, rotating slightly as you adjust the power magnification. Typically, the latter scenario is very subtle and hard to notice without mounting your rifle or scope to a VERY solid surface. Reticle cant can be detrimental to your shooting experience because as you adjust your sight for elevation, the canted reticle is now working your aiming point away from center. Most high-end optics manufacturers would repair this situation for you, but if you bought some cheapo  是 的.Co optic, you may need to replace it in order to take care of the issue. It’s also possible that the cant is very minimal and you can work around it, but you run the risk of being called 之说  时 by your shooting buddies, and nobody wants that kind of attention.

I find the best time to check for these issues is when you are mounting the optic, using the plumb-bob or similar techniques to get your scope mounted perfectly level is also a good way to see if your reticle cants to one or either side. With your scope/rifle firmly (and I cannot stress this enough) fixed to solid point, you can slowly adjust the magnification of your optic to see if the reticle comes out of alignment with your level point. At that point you can make the decision to either send the scope back for service, deal with it, or pawn it off to some poor newb on the Snipers Hide PX.

Turret value

Whether your scope is MRAD or MOA, you can experience TV. And there’s no little blue pill to fix this problem. Turret values are typically 1/10 MRAD or 1/4MOA (yes, I know there are many others but lets be real). How do you know if your turrets click values are actually 1/10? You test it, that’s how. When testing scope’s turret values, I have often found some surprising discrepancies, like instead of being 0.10 MRAD per click, it may be 0.1120 MRAD per click. Is that a big deal? Only you can decide if the discrepancy is worth it to you. If you’re making a 100 yard shot on paper, you will likely never notice the extra 0.0120 MRAD on a click, but if you’re trying to face shoot sod poodles at a thousand yards, and you dial your come up elevation 10 MRAD, you’ll actually have dialed 11.2 MRAD. And when you shoot over him, you wonder why. Maybe your velocity was faster today than when you chronoed it last, maybe your bullet BC is higher than you thought, or maybe the DA lifted two thousand feet because Scarlett Johansson is your spotter.

It can get worse too, turret values can change. Suppose the threads cut inside your scope have a slight gain, or maybe the spring inside is stronger at one side than another. So now that 0.0120 MRAD extra you saw on your first MIL turns to 0.0140 MRAD on the next few MILs. Now you must vary your calculations.

Luckily there is something you can do about it, you can test your scopes turret click value against a good measuring device. Hang a good yardstick at EXACTLY one-hundred yards, and as above make sure your scope/rifle is mounted against a very solid platform (solid enough that turning the turrets causes no movement in anything but the reticle). Using a tool like the Final Scope Level from Short Action Customs can help you in this exercise. Once the scope is mounted solid, you can measure the movement of your reticle against the click value. For example, if you dial one MRAD up, the reticle should come up 3.6 inches. If it doesn’t, then you can do the math to figure out the amount of discrepancy. You can do this across the entire range of the erectors travel, top to bottom. You may find a little movement at either end, or both ends of travel, this is a good reason to use a canted base like 20-30 MOA to avoid running the scope’s erector at the extremes of its travel. All this information should be analyzed, and you can make your decision on what to do about it. I’ll also throw in a shameless plug for our Trasol Ballistic App, which allows you to enter the corrected value of your turret, and the app does all the math for you, adjusting your corrections accordingly.

While you have your scope clamped down would be a great time to check that it comes back to the same spot every time as well. Crank it up all the way and back down a few times and see if it is in the exact same spot every time.

Reticle Values

Reticle value discrepancies are just like the turret ones, and any scope worth having will likely not have them. It doesn’t hurt to check, but more likely you will find problems elsewhere. Calibrated reticles present an entirely different set of issues, since they are only good for a certain bullet at a specific velocity and atmosphere. You can however calculate the actual values of holdover points and assign them the correct value for your conditions. You can also measure them with the yardstick you left hanging out on the fence and find out how many MRAD or MOA they measure.


These are just some of the ways you can test your scope. You’ll also find that doing tests such as these will show you the difference between a good scope and a piece of sh个下.

It’s not always a deal breaker either, but it is absolutely important to know if you are working with an albeit flawed measuring system. Knowing how much can be the difference between a hit, and a miss.

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