The Colt SP6920 is Colt's primary M4 Carbine clone sold to civilians and law enforcement in the United States. It features a 16in. (40.6cm) barrel to avoid classification as an SBR, and is practically identical to the military's Colt M4 Carbines in every other way, save for the lack of fully-automatic/burst fire modes. While they used to commonly be offered with a rail-mounted carry handle sight, most SP6920s have been sold with a simple flip-up rear sight since most owners swap the carry handle out for an optic of some kind, anyway. The particular SP6920 we'll be looking at today has been outfitted with MagPul furniture, an EOTech holographic sight, a flip-away magnifier, and some other accessories which we'll take a closer look at. Let's go ahead and take a look at the rifle itself, however, from the right-hand side.
As mentioned, here we see the SP6920 with several aftermarket features. As you can see here, beyond the optics set-up, this rifle is pretty basic in its configuration. Here we can get an alright look at the EOTech and flip-away magnifier optic configuration, and we can also see that there is a flip-up rear sight tucked away in case those two optics were to fail. We'll take a closer look at this configuration later, but for now, let's start at the muzzle and work our way back.
The Colt 6920 features a threaded 16.1" barrel, and sitting on those threads is something that about any AR owner is familiar with: the M16A2-style flash suppressor. It does a decent job of acting as a combination flash suppressor/compensator. While not the best at either, it's still good enough for government work.
Further down the barrel, we reach the gas block/front sight block, as well as the bayonet lug and sling swivel on its underside. The 6920 is capable of accepting bayonets, but due to its carbine-length gas system and 16in. barrel (versus the M4's 14.5in. barrel), they don't quite fit properly on the rifle as the bayonet ring sits too far back on the barrel rather than resting on the muzzle device.
Here is a bit better look at the front sight block. It is the standard 'A2-style, fixed front sight. Due to the optics on this rifle, we'll go ahead and just take a look at the front sight now.
The front sight post is capable of being rotated up or down in its position in the front sight block. To rotate the sight post, you'd depress the little button at the front of it, then rotate. You can use a bullet tip or a small punch. Each click/quarter rotation corresponds to approx. 1.4MOA adjustment in elevation.
Next we see the Foliage Green MagPul MOE handguard. This handguard is pretty lightweight, and does a decent job at heat dissipation. The little slots you see in it double as Picatinny rail attachment points (or MOE-style accessory attachment points), and also as a cooling feature of sorts as air can get to the outside of the barrel a little bit easier.
This particular 6920 also features a MagPul pistol grip that houses an internal storage compartment. Standard M16/M4 grips do not have a trap door on the grip, and are simply hollow. With the MagPul grip, you could store batteries for an optic, lubricant for internal parts, or Skittles for mid-operations refueling.
The buttstock on this 6920 is also of the MagPul variety. It is a "UBR," and is a type of collapsible buttstock. The top half serves as a cheek pad, while the bottom half moves forward or back to adjust length-of-pull.
To adjust this particular stock, all you would need to do is push the tab on the bottom of the stock rearwards towards the but, then slide the stock half in the desired direction. Once this was accomplished, it would lock itself in place and remain in that position until changed once more.
This particular 6920 has not one, but three rear sights. The order we'll be looking at them is from most advanced to most basic. As you'll see here, there is a flip-away 3x magnifier installed on this rifle. Let's take a look at what optic it's sitting behind first before moving on.
The primary optic on this rifle is an EOTech EXPS3. It can have its brightness adjusted, features a night vision setting ("NV"-marked button), and is powered by a single 123 lithium battery (placed perpendicular to the bore).
Here we see the EOTech reticle (1MOA dot in 65MOA circle) as viewed through the 3x magnifier. As you can see, the front sight post is still fairly visible, but does not present a problem as the dot stays on-target, even if the head is not in an ideal firing position. This is due to the EOTech using a holographic reticle.
Here is the EOTech as you'd see it when aiming with the magnifier out of the way. Again, the front sight is easily visible here, but it doesn't matter as the point of impact is going to correspond with the EOTech's 1MOA dot. What happens when the batteries die, however? Let's take a look.
The MPBUIS (MagPul Back-Up Iron Sight) allows for what is known as a lower-1/3 cowitness. This means that you can use the red dot and iron sights at the same time (cowitness), and that, while doing so, you are looking through the lower 1/3rd of the EOTech's lens. Worth noting, the "starburst" effect from this image comes from my camera focusing on the front sight rather than the target/holographic reticle.
What you saw above was the cowitnessed view of the sights with the small aperture. For close-quarters, moving targets, or low-light shooting with the irons, however, another aperture is available. Folding the MPBUIS aperture down allows you to use this second, enlarged aperture.
Here is a view down the cowitnessed sights of the 6920 while using the larger aperture. As you can tell, it's not quite as precise, but you get a much more open sight picture. This means more light is reaching the eye (allowing better vision when aiming in low-light), and more of the target is visible while aiming. That will come in handy on moving targets or close-up targets where precision is not the biggest concern. Again, the holographic reticle has been distorted due to focusing on the front sight post rather than the target/reticle itself.
So, there you have it: the Colt 6920, and several of its available aftermarket accessories. While the sight system is a bit overkill for some folks, I can see why others would appreciate the ability to have multiple options. However, it does come at the cost of added weight to an otherwise light rifle, and the deployed 3x magnifier can be a bit of a burden when trying to grasp the charging handle. These rifles are pretty nice, however, and are definitely a great first choice for an AR-15 if you're not too sure what direction you wish to go with it: they're a jack-of-all-trades, off-the-shelf rifle, basically. Not necessarily perfect at any one task, but capable of being used for several effectively enough.