On May 11, 2019, the U.S. Army announced that it had chosen SIG SAUER’s 1-6x24mm second-focal-plane (SFP) TANGO6T scope for its squad designated marksman rifles (SDMR). Less than a year later, on January 16, 2019, SIG announced the Department of Defense (DOD) had selected the same scope — but in a first-focal-plane (FFP) version with a different reticle — for use by special operations forces.
Civilians can’t purchase the exact model being issued to the military. However, the only difference between it and the version available to consumers is in the markings.
As might be expected in an optic selected to serve such rigorous duty, the TANGO6T is a robust piece of kit. Built on a 30mm tube, it tips my postal scale at 22 ounces. That’s a bit hefty for an ultralight AR, but it’s a worthwhile tradeoff for the durability, clarity and precision it offers.
I once performed a rigorous technical test and proved that black scopes, when warmed by the sun on one side, actually shift point of impact due to the expansion of the aluminum metal causing a minute change to the relationship of the lenses inside. So I was delighted to see SIG building the TANGO6T in flat dark earth (FDE), which is more sun reflective and less likely to heat to distortion-inducing temperatures. However, for the purists out there, it is also available in matte black.
To cater to a variety of needs, the TANGO6T is available in both the SFP version with the M855A1 reticle and in the FFP version with the 762 Extended Range reticle. It also comes with three additional holdover reticles engineered for a variety of extended-range purposes.
Commercial versions are available in both, but they come only with the lessor accessory kit that accompanies the SDMR scope, specifically, a throw lever, a CR2032 battery, a lens pen and a 2mm hex key wrench. The military versions come with a bunch of other drool-worthy gadgets such as an ultralight ALPHA4 mount, backup iron sights, a padded ballistic nylon cover and more tools.
Let’s take a look at the nuts and bolts common to all the variants:
Clarity and low-light performance is superb, courtesy of extra-low-dispersion (ED) and high-transmittance (HT) glass.
A six-times magnification range — from a true nonmagnified 1X right up to 6X — provides versatility. The low end is ideal for rapid-fire work, and 6X is adequate for precise shooting to quite impressive distances. Not only is the magnification adjustment ring machined with traction that would do a Sherman tank credit, every scope comes with a throw lever that enables fast on-the-fly power adjustments.
To provide a large, bright field of view and a forgiving eyebox, the ocular housing and lens are big. That’s something I don’t like on a bolt action where it can interfere with bolt knob reciprocation, but I’m all for it on an AR-type rifle. A fast-focus eyepiece makes it easy to finesse the reticle to perfect clarity. Thankfully, it turns stiffly and stays put once adjusted to the shooter’s satisfaction (I have no tolerance for fast-focus eyepieces that get easily turned).
Atop the scope is a low-profile capped elevation turret. Depending on the version, clicks are either .2 mils or .5 MOA. The test version pictured here is mils and offers a full 20 mils of adjustment per rotation.
Horizontal point of impact (POI) is adjusted via a similar turret on the right side of the optic. On the left is a battery housing and 11-position rheostat that controls the brightness of the illuminated reticle. It’s locking, a feature that I really appreciate. Pull to turn, push in to lock. An “OFF” position between each brightness settings enables easy shutdown without having to run clear through the spectrum of brightness. And for those to whom it matters, there are two night vision (NV) settings.
Interestingly, a laser-engraved mounting reference line is etched into the left side of the scope tube just forward of the illumination rheostat turret. This makes it easy for anyone from professional armorers to average Joes to mount a TANGO6T nice and level. Just line up that mark in the left-side scope ring gap and torque the mounting screws to spec.
Clearly, the scope is given above-par waterproofing. It’s IPX-8 rated for complete and continuous immersion at 20 meters. That’s a bit more aggressive than most waterproofing protocol calls for. It’s also rated fog-proof internally. Any scope’s exterior lens surfaces can temporarily fog up in cold temps if you breathe on them.
Also appealing is the fact that the SIG TANGO6T is assembled in Oregon. Optical components are covered by SIG’s Infinite Guarantee. That’s pretty much what it sounds like: unlimited. Electronic components are covered for five years.
Intriguingly, the scope is built using SIG’s STEALTH ID deflection armor trapezoidal surfacing to break up the shape and visibility of the optic.
Lenses are protected with a Mil-Spec “oleophobic” coating, which helps prevent oil, gunk and even water from sticking. Abrasion-resistant “LENSHIELD” coatings minimize scratching and other performance-inhibiting damage, and “SPECTRACOAT” anti-reflection coatings maximize light transmission and image purity.
Because a scope and rifle deserve each other, I mounted a TANGO6T test unit on my favorite AR-15, a customized lightweight DMR-type carbine built using an 18-inch Proof Research barrel, Battle Arms Development receivers and stock, BCM rail, LanTac bolt carrier group and Timney trigger. It’s a solid half-MOA rifle with its preferred ammo, which is Black Hills’ 77-grain TMK 5.56 NATO load.
I didn’t have a SIG ALPHA4 Ultralight mount, so I mounted the scope in one of Leupold’s excellent Mark 2 IMS mounts, which is a one-piece base/ring setup that holds the scope wonderfully secure. It’s perfectly machined, so the inside of the rings needs no lapping to grip the scope’s tube evenly and without distortion. Also, it has a long, sturdy mounting surface that can securely bridge forward from the front of the flat-top receiver rail and grip the rail atop a handguard.
Although this test TANGO6T scope’s reticle is nominally designed for use with 7.62 extended-range ammunition, a 77-grain Sierra TMK sports a ballistic coefficient (BC) of .420, which is relatively similar to that of various .308 Win./7.62 NATO 168-grain projectiles, and it exits the muzzle of my AR-15 at 2,700 feet per second (fps), which is also similar to the 7.62. At any rate, I decided to work the reticle out with the 77-grain 5.56 load just for kicks and see how it lined up.
The SIG owner’s manual that accompanies every scope provides a detailed description of the reticle. It’s engineered for meters rather than yards and features wind-hold-dots calibrated for a 10-mph full-value crosswind. Each holdover line is calibrated to span 18 inches at the distance which it represents. This means, in plain language, that a soldier can measure distance by simply bracketing an enemy’s shoulders to find a line that more or less fits then hold center mass using that line and most probably achieve an impact.
When paired with yards, the 77-grain TMK and the 762 Extended Range reticle don’t fit well. Switching the calculator to meters, which I don’t prefer but can deal with, lines ballistics up a lot closer. By keeping the temperature at the standardized 59 degrees Fahrenheit but adjusting the elevation to 3,000 feet, the load and the reticle line up almost perfectly.
I live at 5,000 feet, but I can work with that. Reticle calibration is close enough for government work on predators to 600 meters and is easily extrapolated for more distant work.
It took three groups to get point of impact married to point of aim. I’d anticipated that I wouldn’t be able to hold the sub-half-MOA groups the rifle is capable of when mounted with a high-magnification target scope, but to my delight, three consecutive groups measured .49, .53 and .3 inch, respectively, a .44-inch average.
Being a FFP reticle, the holdover hashes nominally work at any magnification. I couldn’t really see them well enough to make good use of them at less than about 3X, but that’s fine — any time I’m going to attempt a long shot, I’ll have the magnification cranked all the way up to 6X.
With my zero refined to perfection, I shifted positions while holding center on a 600-yard steel torso with the “6” holdover hash line. I fired. A first-round impact dead center on the target was the result. With a shooting buddy watching through the spotting scope, I hammered four more shots into a group centered on the target. All five spanned a shade less than 6 inches, and four of the five impacted inside a 4-inch group.
Candidly, I was a bit giddy with that level of performance. At the risk of seeming melodramatic, I simply can’t find anything wrong with this TANGO6T scope. Typically, I can temper an enthusiastic in-depth technical review with some subjective but frank observations on what I believe might be improved. This time, I’m at a loss. For an all-around AR-15 scope, it’s darned near perfect.