Metrics That Matter - Test Tracking On Scopes
June 23, 2017
Riflescopes are amazing pieces of equipment that perform an essential task: They allow us to clearly see and accurately shoot at our target. The past five years have brought an avalanche of improvements in the riflescope department. Now we have so many quality options that it's hard to make a choice.
Couple the number of options with the price tag of top-of-the-line models, and we have a surefire recipe for paralysis by analysis.
In an effort to help the hard-working, underfunded sniper, this article is solely about testing scopes. The tracking/canted reticle test discussed here is easy to conduct in the field without special targets or jigs (shooting stuff should be fun).
METHODS AND MADNESS
There are many ways to test tracking on scopes. Some testers lock the scope in a jig and watch what happens to the crosshairs as they twist the turrets, while others use tall targets where they shoot one round, dial, then shoot again. This happens repeatedly. Both systems have their merits. Both systems also have their drawbacks.
The jig-user has to build the jig (which is a pain and can create problems of its own). The jig test also relies on video footage for the tester to have any way to pass on the results. The interwebs have a couple of guys doing these types of tests, and they are an excellent source of information, provided the tests are taken in context.
One scope tracking well is no guarantee that others will do the same. The videos to look for on the Internet will test more than one sample over an extended period of time. This is information worth having. However, I watched scopes perform well on a couple of these types of tests that then had a mediocre performance when I tested the same model on a rifle. There is no substitute for doing your own fieldwork.
Tracking errors are usually present throughout the turret's adjustment range. Think of it as being off by a certain percentage. Often, it will take several mils or minutes of adjustment before the scope error will show up. Very few scopes will have tracking errors that occur with less than 5 mils of adjustment. The tolerances must have a chance to stack before we can see if there's a problem. If we're just looking through our scope, we may or may not see the problem.
Shooting tall targets is another way to test tracking. We prefer this type of test because it leaves empirical evidence that we can later measure, but we don't particularly care for printed targets.
It's difficult to get printed targets onto the backer board tight enough that the printed measurements subtend in actual mils or minutes. Backer boards are never perfectly flat or rigid, so the sag or curvature can throw off our measurements. If you use printed targets and find that most of your scopes add elevation to what you dial, it's likely the target/backer
board caused the problem. Getting 3 feet of paper target perfectly flat, stretched out as tight as when it was printed and then attached to a target backer is not easy.
For our scope tracking test, rigid white foam board material or the white corrugated plastic boards from any of the big office supply stores are a great
choice, and you can draw on it with a Sharpie. It doesn't sound very sexy, but it's easier to get accurate measurements with this
method than using paper targets. The rigid material is much more robust than cardboard or poster board, and it doesn't sag under its own weight or disintegrate when wet.
We draw one horizontal line the width of our board about 3 inches from the bottom. Put a small point on the horizontal line 2 inches on either side of where we want our vertical line. Using a geometry compass, place 3 inches of space between the compass pencil and point, and draw a circle around each point on the horizontal line. Use the level to bisect the two points where the circles intersect (this must be precise for this method to work) and draw the vertical line the length of the whiteboard. This method ensures that our lines are perpendicular. This step is important because it will reveal whether or not our reticle is canted. This sounds a lot like math class right now, but suck it up and bear with us.
If you don't mind buying a couple of basic drawing tools, a faster method is using a T-square. Since the corrugated plastic and foam board material is laser cut, the sides and edges are perfectly square. Slap a T-square at the bottom and side of the board and draw a couple of lines. Voila! A perpendicular set of lines to do a scope-tracking test.
Most levels have inch measurements along one side, so use that to draw a 3-inch horizontal line every 3.6 inches along the vertical axis (if testing a mil/mil scope at 100 yards). If the final short horizontal line is 11 mils, double-check to see that it measures exactly 39.6 inches from our aiming point. Place the poster board on the target stand, and clamp your level along the horizontal axis, leveling the target in the process. Lastly, get a measuring tape and measure 100 yards from our firing point to the target stand. Most rangefinders are close at 100 yards, but none of them are as accurate as a tape measure. Try to borrow one. You only have to measure your testing location one time, so buying a tape measure might not make much sense.
Our test protocol is to dial 1 mil, aim at the intersection of the horizontal and vertical line, and fire one round. Our aiming point will always be the horizontal/vertical line intersection. It is also important to level the scope for each shot. A fast way to level the reticle is to place the horizontal stadia along the top of our level while holding our crosshairs on our aiming point. I like to use a bright orange level to contrast nicely with a black reticle. This method also obviates the need to have a scope level on every optic you test and speeds up the process.
Continue to add 1 mil and fire one shot until you get to 10 or 11 mils elevation. This is at the edge of the poster board. After firing a round at max elevation, remove 5 mils from the scope, add them back on and fire another round. Five mils is arbitrary; the important thing is to twist the turret between every shot. Subtract 1 mil and fire a round, repeating the cycle as necessary until you're back to our zero. Continue the test until you have three rounds at each mil of elevation.
WHAT'S IT MEAN?
Provided we paid attention to the details and leveled our scope for each shot fired, we now have some mighty fine empirical data on our scope.
Many don't realize just how much scopes of the same model from the same manufacturer can differ. Just because one scope tracks beautifully and has a plumb reticle is no guarantee that they all do. No matter whose name in on the side of the scope and whatever stellar reputation they might enjoy, we should be professional enough to check our equipment. As The Great Communicator often said, "Trust, but verify."
Two common scope issues are inaccurate tracking and canted reticles. This test accurately checks for both problems. Most scopes will track well for 5 or 6 mils. Once they get past that distance, tolerance stacking starts to kick in, if there is any, and our groups will get increasingly farther away from our earlier groups. An example would be everything looking good elevation-wise until 7 mils, where it's a little high. It's higher still at 8 mils, and then at 9 mils it's a full .1 or even .2 mils higher than it should be. That's what tolerance stacking in a turret looks like, and it's hard to spot unless there are holes in paper to measure
Since our horizontal and vertical target lines are perpendicular, this test can determine if our reticle is canted. As an example, let's say our groups are all just high and right of each horizontal/vertical line intersection. Provided they all stay in the same place relative to the intersection, our scope tracks beautifully and the reticle is straight. If they start on the right side of the vertical line and veer over to the left, our reticle is canted enough that we should return it.
Canted reticles can be hard to spot. By the time they start posing problems, we're shooting far enough away that it's easy to assume we misjudged our wind call. We've heard of checking for a canted reticle by putting a level on the elevation turret, leveling the scope, and then checking the reticle against a level or plumb line downrange. This method is crude because it introduces variables from the external dimensions of the scope and requires leveling based on a small surface (the elevation turret).
KEEP IT SIMPLE
Given the disparity of one scope's performance to the next, we should make an effort to verify that the scope we deploy with performs as advertised. Doing so gives us invaluable information about the unique characteristics of our scope, as well as confidence in our equipment. Confidence that carries us through a crisis or a deployment is a hard thing to come by, so spending time on the range getting to know our scope is time well spent.
The consumables needed to run this test can be purchased for just a few bucks. Most of the tools mentioned in this article are probably already in your garage or a buddy's.
Once you test your scope, either take a picture of the target board or write up a summary of your findings. Your test is a crucial data point for any sniper and will allow you to share what you found with other professionals who would appreciate the information.