Rock That Glass! Getting the Most out of Your Variable

Rock That Glass! Getting the Most out of Your Variable

My first variable, a Vortex Viper PST was a decent optic and had good qualities, but ultimately I sold it since it was too heavy. In actuality, my rifle was the pig. I didn’t know how to really get the most out of the Viper PST at the time, and the amount of ballistic study I did behind the viper was minimal. I went to the ACOG and now I am back full circle with a variable again: The Razor HD II.

Before I sold my Viper PST, I wish I had someone show me all the things I am about to share with you… I might not have sold it. Today we are going to look at all the ways variables can be used to give you an edge; let’s learn to use them to their max potential.

There is No Spoon:

Most low magnification variables are second focal plane. This means that the reticle stays the same size through all magnification levels. Typically, the highest level of magnification is used for ranging. My Razor HD II is made to range 9 inch wide targets at 6x zoom out to 600 yards; the optic is calibrated for a good “all around” bullet drop, but seems to fit 75 grain ammo like a glove. Nothing that I shoot matches the BDC exactly, but if we adjust the magnification, we can do some really neat things to the BDC calibration. By adjusting the magnification of a second focal plane scope, we can tweak the drop to better match our loadings. In some cases, you will find multiple loadings that can be a darn near perfect match! Check out the example below:


My 60 grain Varmint Loading calibrates to my optic at 5X. The optic is calibrated for a faster/ higher BDC projectile, but I can modify the BDC to work better with different loadings at different magnification levels. What’s even spookier… is that with the JM-1 BDC reticle, a 10.5 blackout running 2200 FPS 110 grain ammo is *perfectly* calibrated at 3x for both stadia width and height out to 600 yards.

The above example is an awesome way for me to get more out of my optic.  I found that several of my loadings can be adjusted to the BDC on a vertical axis by just sliding my zoom to 5 or 5.5x. This skews my horizontal stadia width a tiny bit, but it’s still useful. This capability certainly helps since some of my loadings, such as the 60 grain Sierra Varmint referenced above, were not designed with my reticle and were a poor match, but now I can adapt to the loading easily. I found that this technique only helped match my BDC when the projectile flies slower / has a lower ballistic coefficient than the load the optic is calibrated for.

Lock It Out:

Variable Scope Cat Tail

Loosen your cat tail and turn the variable to the magnification level you want…

Variable Scope Cat Tail 2

and rotate it until it bottoms out on the mount. Locked it in place and now we are locked out of 6x.

So now that we found a new way to use the BDC of our variable, we need to lock it out so that we can use this “feature” when we are shooting our secondary loading. If you have a cat-tail, simply dial to the appropriate magnification level and loosen the cat tail. Rotate the cat tail so that it buts up against the rifle / mount and re-tighten. Viola! You have locked your variable out at the magnification that suits your loading. This will be useful if you are at a competition and don’t want to rotate past your new settings. What is the cat tail I am using? I don’t know, it’s some kind of fishing thing, but it works great on variables.

Know Where the Light Is:

Optics funnel light into your eye. All optics do. What they don’t all do is gather the light efficiently and not all optics are tunable to your personal pupil diameter. A variable is “tunable” and allows you to adjust the exit pupil size as you magnify the image.

As you turn an optic’s bell to zoom in on the target, the exit pupil shrinks in size. On a variable, the exit pupil at 1x is larger than the diameter of our pupil and light spilled around your eye is wasted. Not a big deal since in daytime our pupil is only a few millimeters open anyway. As light dims and our pupil opens up, we need to adjust the optic for maximum low light performance.


Our perceived image brightness gains until we hit 3.4x zoom with the MTAC, enhancing the perceived brightness of the image 2.21 times and slowly declining from there. The larger the objective of the optic, the higher the perceived brightness will be as you turn up the magnification.

In low light, our pupil opens up to 7-8mm in size. Adjusting the optic to match our pupil will give us the greatest gain in perceived light gathering ability. I found many variables seem to have that  low light sweet spot around 3.5x. You don’t need a calculator to figure out where your 7mm setting is, simply take a caliper, adjust to 7mm and adjust your optic until its size matches the caliper diameter. Mark down the setting. Viola: You have increased your low light capability with your variable.

Variable Scope Exit Pupil

Adjusting your bell to a higher magnification focuses the exit pupil. Making the exit pupil match the diameter of your night adapted pupil will allow the maximum amount of light to reach the retina and stimulate as many rods and cones as possible: The Net effect is a brighter image. Measure to 7mm as a good starting point.

Adjusting Impact:

What would you do with the following picture? Note: The subtensions are listed to the left and start below with the first line below the cross-hair. The horizontal MOA from the center to the thick line is 15 MOA.

Vortex Razor HD II MOA drop

The target is… huge, but is only an example. Here we can adjust our impact as long as we know the values to our BDC. If you have a MOA or MIL based reticle that is not calibrated to a particular loading, this is much easier.

If we use our optic at its calibrated magnification, we can adjust our dope based on point of impact. In my case, shooting at this ginormous target… it seems I need to come up about 5.5 minutes and adjust windage around 8 minutes. If you have a reticle with elevation and windage stadia in fixed non-caliber specific increments, then this becomes even easier. Or you could use the BDC if your load matches… but understanding other ways to use the reticle is only to your benefit.

Strelok +: A Good Companion


If you don’t have Strelok + yet, getting it should be priority #1. It has tons of built-in features and reticles for a myriad of optics. It gives you a visual representation of drop, windage, and is extremely versatile. I get no payment or help from the developer, I had to buy it on the app store just like everyone else… but the value has been INCREDIBLE. Having this tool has given me tons of data and added more versatility to my optic.

Another essential tool is a log-book. Getting the most out of a variable will be far easier if you keep track of all the loadings that you send through the barrel. With a good log book, you can record point of impact shifts for different brands of ammo and save that to adjust your scope for many different reference loadings.

Log Book Rite in the Rain

I should have kept a log from the first day I decided to pursue my marksmanship goals. This brand of target and data book is Rite in the Rain and it’s waterproof. Handy to keep around!

Wrapping Up:

As I said at the beginning: Had I known more about my first variable, I would still have it. With the knowledge I have gained over the years, I can make better use of a variable for my shooting. My Razor HD II is a substantial upgrade from the Viper I initially had. With this new variable and my range experimentation, I expect I will develop an awesome set of data and loadings that will allow me the greatest value of my glass investment. Experimenting with a good ballistic calculator and searching for ways to get the most out of your variable will impart upon you some excellent results. Happy Shooting!

Bonus: Here is that .300 AAC I mentioned, and it lines up spooky good at 3x for a 110 grain loading traveling near 2200 FPS from a SBR.


Written by lothaen

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