September 23, 2010
Selecting the proper optic to mount on top of a tactical rifle can be a daunting task.
Selecting the proper optic to mount on a tactical rifle can be daunting, but keeping David's suggestions in mind should help you find the scope that best suits your needs.
Perusing catalogs and websites will turn up a staggering array of riflescopes intended for military, law enforcement, and serious civilian use. Because the offerings range wildly in design and price, it can be very difficult to wade through what's available and settle on a particular model. This month I'll offer a few tips to keep in mind when trying to choose the right tactical scope for your new precision rifle.
Before you even select a rifle, I suggest sitting down with a piece of paper and asking yourself some questions. How you answer will serve as a guide for selecting the proper optic for your needs.
Things to consider:
Will it be used for true professional use (law enforcement or military) or recreational use (long-range shooting, sniper-type matches)?
At what distances do you expect to do 80 percent of your shooting? Be realistic.
What will your maximum range be?
How much of your shooting will be at dusk, dawn, in low light, by moonlight, or with the aid of a separate light source?
What is the caliber of your rifle?
What are the weight and length of your rifle?
Will it be deployed with an ancillary night vision device?
How much did your rifle cost, and how much do you have to spend on an optic?
Answering these questions will give you a better idea of the type of optic best suited to your individual needs. Just be brutally honest with yourself. Keep in mind that any optical instrument is comprised of a number of compromises. There is no "perfect" scope that is the optimum for everything. So you must decide on what features best suit your needs.
The first place to start is deciding if you need a fixed- or variable-magnification scope. Military scopes traditionally have been fixed power. The strengths of a fixed-power scope are that they are more robust, easier to make fog- and waterproof, have fewer lenses (so are brighter than an identical variable-power model), and tend to be less expensive. The downside to a fixed-power scope is its lack of flexibility. With a variable-magnification scope you can power down to increase field of view (FOV) and/or to enlarge the exit pupil to brighten the image. With recent improvements in design and manufacture, variable-power scopes are now robust enough for serious professional use. Because of these advancements, I believe the days of a fixed-power scope on a precision rifle have come to a very definite end. I strongly recommend a variable-power scope.
You need relatively little magnification to shoot effectively. On full-size silhouettes 4X gives good results at 500 yards, 6X is effective at 700 yards, and 10X works well at 1000 yards. Too much magnification, on the other hand, can be a serious liability. A small field of view and mirage can both cause problems. So does that mean anything over 6X to 10X is bad? No. While hitting a white LaRue target at 500 yards is simple with a 4X scope, locating and identifying a hidden target at the same distance is a different matter entirely. Higher magnification can be a useful aid in this regard. One of the advantages of the modern variable-power scope is the ability to collect information on a higher magnification and to power down to engage targets on a lower magnification.
What magnification range should you consider? This will depend upon your individual needs, but I think most riflemen are well served with a simple 2.5-10X. A scope in this magnification range provides a large FOV at 2.5-4X for close-range shots on moving targets. Powered up to 8-10X, it has sufficient magnification to identify and engage targets at long range. If your needs dictate jumping up in magnification to 16X or 24X, keep in mind that higher magnification means less FOV and a smaller exit pupil. (I know some prefer a 6-24X scope to use in place of a spotting scope, but the problem with this usage is that few riflescopes can match the resolution and brightness of a high-quality spotting scope.)
Turret adjustments should be distinct with tactile and audible clicks. Most important is the need for the scope to track consistently throughout its adjustment range.
When choosing the magnification range of a variable scope you must also take into account the ambient lighting conditions. Why? Simply because magnification and objective lens size need to be considered together as they interrelate. If you never plan on shooting in any conditions except bright light, this is not an issue for you. For the rest of us exit pupil size is very important. Ideally for low light use you want your scope to generate at least a 6mm exit pupil that will allow you to locate, identify, and engage your target. Exit pupil is calculated by simply dividing the objective lens diameter by the magnification. As an example, a scope with a 40mm objective lens set at 10X generates a 4mm exit pupil. Power that same scope down to 5X and it generates an 8mm exit pupil.
Also, theoretically, the larger the objective lens the better the resolution (all things being equal). Enhanced resolution is a useful aid when shooting under low light conditions.
Objective Lens Size
While I have shot very well under moonlight using scopes with 56mm objective lenses, please keep in mind that large scopes have drawbacks. They're heavier, bulkier, and easier to knock about. Plus, the larger the objective lens the higher the scope will need to be mounted above the bore. From a tactical standpoint, the larger the lens the more likely it is to reflect light and disclose your position.
Tactical scopes are commonly available with 1-inch, 30mm, 34mm, and 35mm tube diameters. Generally, the larger the tube diameter the more robust the tube is and the more adjustment the scope will have. Larger tubes with thicker walls also add weight, so there is no free lunch. By far 30mm is the most common diameter on tactical scopes, with Schmidt & Bender offering 34mm and I.O.R. offering 35mm models.
Mounted to the tube will be the scope's mechanism block wi
th the windage and elevation turrets. These control the ballistic adjustments you dial into your scope. The turrets should provide very distinct audible and tactile clicks so you can easily keep track as you make adjustments. Scopes are commonly available with 1/4-, 1/2-, and 1-MOA adjustments and some offer models with 1/2 and 1cm adjustments. I find 1/4-MOA adjustments too fine for field use and 1-MOA adjustments on the coarse side. I prefer 1/2-MOA adjustments because they cut the number of clicks one has to make (and keep track of) in half. If you are willing to range in meters and do all your ballistic and Mil calculations in metric, a scope with 1cm adjustments will also work very well. I prefer capped turrets, a positive zero stop with all elevation in one full turret rotation. The adjustment range of the scope should be more than enough to reach your maximum desired range with your load of choice.
When choosing a tactical scope, David recommends picking a rugged design with reliable adjustments, superior light transmission, and excellent resolution.
It seems as though everyone has a proprietary tactical reticle today, so wading through all of them to find one that's right for you can be difficult. Instead, focus on your actual needs and then pick a suitable design. To start, a reticle needs to have a definite easy-to-define aiming point that is plainly visible in low light or shadows. It should also incorporate at least one method for quick and accurate rangefinding. Holdover and lead marks can also be useful, but the last thing you want is a cluttered FOV. Whatever you decide on for a reticle, I strongly suggest you opt for an illuminated version. Properly utilized it will greatly aid low-light shooting.
Should the reticle be in the first or second focal plane? Again, this is your choice. There are pros and cons to both designs. A first focal plane reticle can Mil or rangefind at any magnification. A second focal plane reticle is easier to employ on low magnification and in low light.
When it comes to parallax adjustments, side focus knobs are currently the rage. Despite this an adjustable objective (AO) has the advantage of being both more precise and more robust. In many ways it's the better design, but AOs are no longer hip and are rapidly fading from the scene. I do recommend a European-style fast focus eyepiece. This is a nice feature to have.
While the perfect tactical scope does not exist, there are some very good designs available. I recommend carefully evaluating what your needs are then picking a professional-grade optical instrument from one of the top-tier optical manufacturers. Once you acquire it don't forget to test it to ensure the tracking is true. Then practice with it so you know it intimately.