The Sig Sauer BDX System

Designed to simplify practical long-range shooting in field conditions, SIG SAUER’s BDX system uses Bluetooth to pair the company’s rangefinder with a ballistic app on your smartphone and a BDX riflescope. The three work in concert to provide a ballistic solution and an easy holdover point. No turret dialing, no counting reticle hash marks. Just range, aim, and squeeze.

When in use, the rangefinder determines the distance, references wind direction and strength you’ve manually input via the smartphone app, and wirelessly communicates a ballistic solution to the scope. In fractions of a second, an orange holdover dot appears on the crosshair’s vertical stadia and—if applicable—a wind hold dot on the horizontal crosswire.

The choice of orange is important. Unlike red dots, orange dots can be seen by color-blind shooters.

Critically, the rangefinder measures temperature and altitude and plugs their effects into the calculated solution. Also vital: The rangefinder and scope will work together without the phone present. However, without the phone app, the system doesn’t provide suggested wind holds.

To understand what the BDX is really capable of, it’s necessary to be familiar with each piece of the puzzle.

The Rangefinder

When introduced several years ago, SIG’s KILO2400ABS rangefinder kicked the competition aside and stormed the market. At the time, nothing else was as compact or as capable.

The KILO2400ABS possesses a powerful ranging engine. It measures ballistic-curve-distorting atmospherics in real time, on-site. Angle compensation? Naturally. And it Bluetooth-pairs with SIG’s smartphone app to upload refined ballistic rifle/projectile profiles and uses an embedded version of the renowned Applied Ballistics calculator to compute holdover solutions.

Each KILO2400ABS includes a wind meter compatible with smartphone jacks. Once your phone captures wind speed and heading, the system also provides a wind compensation solution.

However, the KILO1400BDX ($300) and KILO1800BDX ($480) rangefinders compatible with the BDX system do not have that same capability. Not quite. Rather than reading actual, on-site air density, they operate off of simpler altitude and temperature measurements. And unlike today’s really sophisticated ballistic apps, it cannot compensate for projectile spindrift, aerodynamic jump, or Coriolis effect. Wind strength and heading must be entered manually via the smartphone app.

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It’s important to understand up front that the BDX is designed to be a practical system for use within practical limits. Maximum effective range is 800 yards. Inside that distance, spindrift and Coriolis effect and the other infinitesimal refinements so critical to first-round impacts at extreme distances don’t have much effect.

What KILO BDX rangefinders do is zap targets quickly and reliably. Lasered ranges are the average of several sophisticated measurements derived via SIG’s Lightwave DSP ranging engine and tend to be extremely accurate. The display uses Lumatic auto-adjusting brightness that compensates for varying light conditions. Shot angle, temperature, and altitude are measured and compensated for. And using onboard Applied Ballistics Ultralight—a simplified but capable ballistic calculator—it computes a holdover solution, and Bluetooth communicates to the BDX scope just where to illuminate that lovely orange holdover dot.

The Smartphone App

SIG’s free BDX smartphone app is primarily used to set up a ballistic profile—meaning the particulars of your rifle, projectile, muzzle velocity, scope height, and so forth—and export it to the KILO BDX rangefinder. After that’s accomplished, it’s primarily helpful for inputting wind speed and direction. If you end up purchasing two or more BDX scopes for various rifles, the smartphone app is also used for switching ballistic profiles and pairing with the appropriate scope while in use.

The Scope

Because I was already quite familiar with SIG’s KILO2400ABS rangefinder, I knew what to expect from the BDX rangefinder. The scope, however, surprised me with its plethora of innovative features.

To begin with, it’s a standard-size optic, not a gargantuan monstrosity that makes a rifle top-heavy. Several different-size variations are available, including a 3.5-10X 42mm ($599, 21 oz.), a 4.5-14X 44mm ($720, 23 oz., tested), 4.5-14X 50mm ($840, 25 oz.), and 6.5-20X 52mm ($960, 26 oz.).

Its magic comes from Bluetooth compatibility and the BDX-R1 digital reticle, which is what displays the orange aiming dot. Importantly, while the reticle itself is on the second focal plane, the computer’s brain is on the first focal plane, meaning that the scope’s magnification setting doesn’t matter—the dot will be accurate no matter what power you’re zoomed to. It’s worth noting that the wind-compensation dots activate only above a certain magnification level—10X with the 4.5-14X 44mm version I tested.

A tiny blue LED is embedded in the rear face of the magnification ring’s fin and shines steady blue when the system is active. When woken, it flashes briefly blue as it acquires a connection with the KILO BDX rangefinder. It also flashes when fresh data is imported, such as a new range. Several rheostat settings with “off” positions between each enable the user to refine brightness to fit ambient light.

Critical to precise long-distance shooting, a parallax focus ring is housed between the rheostat and the turret base.

One of my favorite features is the Auto LevelPlex, which is a pair of upward-pointing orange triangles inside the scope, one at each extreme edge at 9 and 3 o’clock in the field of view. If the scope is canted, whichever side needs to tip up flashes, the orange triangle indicating the direction to move. According to SIG’s literature, the farther the ranged shot distance, the more sensitive the digital level becomes. It’s a nice feature that allows fast shooting up close where a bit of cant doesn’t matter, yet provides the precision necessary way out yonder.

Another innovative feature is the KinETHIC kinetic energy transfer indicator. Based on projectile weight, muzzle velocity, and ballistic coefficient, it calculates the distance at which impact energy drops below ethical levels. Said minimum energy levels are not arbitrary—the shooter inputs them manually via the BDX smartphone app and thus may adapt the level depending on the game currently being hunted.

My first concern when becoming familiar with the BDX system was turning on all the gadgets quickly enough when a surprise shot opportunity presented. I needn’t have worried. The scope’s system is motion activated, so it’s always on while stillhunting and simply picking it up from the corner of a stand brings it to life. The rangefinder activates Bluetooth as soon as the range button is pressed and pairs within seconds.

Entirely aside from intriguing innovations and features, the BDX scope is well built. Glass surfaces feature SpectraCoat, which is a top-notch anti-reflection layer that enhances light transition and color purity. Lenses are well ground, resulting in minimal distortion. And it’s internally fogproof and is waterproof to 1 meter.

Field Tests

To put the BDX to work, I mounted it on a Remington Model 700P LTR in .308 and built a ballistic profile for the 168-grain Hornady match bullet the rifle shoots best. Then, from the prone position, I shot various steel targets out to almost 800 yards. I made first-round hits on most targets.

Two days later I switched the Sierra3 BDX scope to a friend’s Browning X-Bolt Long Range McMillan rifle in 6.5 Creedmoor, and we worked it out to 730 yards, making first-round hits even more easily because of the 6.5 Creedmoor’s superior wind-bucking ability.

My friend drew a coveted Utah elk tag for this fall, and the effectiveness of the system quickly had him lusting for one of his own. Who knows, I just may loan him mine. A sterling tag like that deserves a stellar optical system like the BDX.

The BDX system is not for competitive shooters. It’s a tool for hunters and makes practical field shooting to several hundred yards easier. In practice the BDX system is profoundly simple and effective—more so even than it seems while learning and setting up the various components.