Ready to do some long range shooting? Now that your rifle is properly set up, your scope is perfectly zeroed (if not, don’t worry, just check out these posts first: How to Zero Your Scope and How to Zero Your Scope – Part 2; I’ll be right here when you get back). If you’ve been following this entire long range series, by now you are probably impatient to go the field and try to engage some targets from a distance. But there are there two important checks that you need to perform before you’re completely ready to rock with your precision long range rifle; you need to verify vertical scope symmetry and click values. These two preparations are often skipped over as non-essential for hunters and short range shooters. However, if you want to get the absolute best out of your long range rifle system, you’ll want to pay attention.
Why It’s Important
If the scope’s vertical axis is not perpendicular to the rifle’s bore axis, when you turn the elevation knob to compensate for drop, you won’t be compensating vertically and following the trajectory, Instead, you’ll be compensating at an angle from your projectile’s trajectory. In addition, if you use your reticle as a reference to keep the rifle perpendicular to the ground, you’ll also introduce an error into your accuracy, as we found in the article on rifle cant error.
“Truing” the click value is also important. Every scope comes with a declared value of adjustment for every click of elevation and windage, such as, for example, ¼ MOA, or 0.1 mil per click. Often, the declared value doesn’t correspond precisely to the actual value that you obtain from the mechanics installed in the scope. This especially likely with low-to-mid price scopes. The difference from the declared and the actual value is subtle, often only a 5 to 10% discrepancy. For the average user, shooting from 300yds, the error will be largely unnoticeable. But we are long range shooters who”re going the distance, so to speak, and distance amplifies everything. If your ballistic table says that you need 40MOA to hit the target at 1000yds, and you dial the 40MOA on the elevation turret without considering a 5% error, you will actually be dialing 38MOA. That 2 MOA at 1000yds are translates to 20in, which is a miss on most targets.
Luckily, with a single target and a couple of rounds, you can easily verify both scope symmetry and click value.
You’ll need to start with a paper target of at least 50inches tall, a plumb bob (or a bubble level), a ruler and a marker. After you have zeroed your rifle, place the target at 100yds. Next, using the bubble level or the plumb bob, draw a straight vertical line along the entire target height. After that, draw a dot, no larger than one inch, on the vertical line at about 5 inches from the bottom of the target (I use the sticky repairing dots that come with Birchwood Casey’s Shoot-N-C targets for this purpose). With the ruler, measure 42 inches from the dot to the top of the vertical line, and draw a mark. Now you’re ready to shoot.
First, keeping the scope’s reticle parallel to the vertical line on the target, shoot at the dot on the bottom, to verify the zero. The next step is to dial 40MOA on the elevation turret and fire three rounds, always aiming at the dot on the bottom of the target, while holding the vertical line of the reticle parallel to the vertical line on the target. If your scope is mounted perpendicular, and the click values are true, your group will be centered on the vertical line and on the mark you put at 42in. If the group falls off the vertical line, you’ll need to adjust the scope symmetry by rotating it clockwise if the group falls to the right and, vice versa, counterclockwise if it falls to the left.
The click value should be verified only once you have obtained a proper vertical alignment. When you do have proper alignment, you can measure the actual distance from the dot to the center of the group and take it as a reference for your true click value. You just need to divide that distance for the number of clicks you dialed. Many ballistic softwares, including JBM Ballistics, which we will be using as a reference in this guide, offer the possibility to set a specific “true click value” so your ballistic table can be “tuned” to your scope.
If your scope has mil turrets, to simplify the process, I suggest carrying out this test at 100m (instead of 100yds), setting the reference mark at 100cm (instead of 42in) and dialing 10mil on the elevation turret.
Finally, your weapons system is perfectly set-up for the long distance. The only thing you need now, is a ballistics table. In the next article, I’ll show you how to use the JBM software to create your own. Stay tuned!