In this post, I’m going to discuss the Combat Shooting and Tactics Rear Aperture Sight, designed by Paul Howe and available from XS Sight Systems. The CSAT rear sight can be installed in many typical AR rear sight bases, and a Troy BUIS specific version is also available. The Troy version is available either as the sight blade only, or in a complete rear sight.
Paul Howe designed the sight to allow shooters to use their carbines at varying distances without flipping between the different apertures of a typical AR rear sight. In addition, the sight design allows for a carbine or rifle to be quickly and easily zeroed at 7 yards, and then at 100 yards. The rear sight features a peep aperture with a notch cut into the top of the blade. The notch is designed to be used at close distances to accommodate for offset, and the peep aperture is designed for traditional use at longer ranges. If this doesn’t make sense, consider that the typical height of the sights over the bore of an AR necessitates a higher point of aim at close ranges to have an accurate point of impact. A hostage shot at room distance requiring a central nervous system hit is the typical example used in classes. To make that shot with normal sights or a red dot, you have to hold approximately 2 inches above your intended point of impact. With the CSAT rear sight, you simply use the notch like pistol sights, by placing the front post in the notch to yield accurate hits at close ranges. When using the notch, your point of aim will be your point of impact. At longer ranges, simply use the peep aperture. In an explanatory video, Howe uses the example of needing to transition from a parking lot to a classroom to a long hallway in a school. Further, Howe suggests zeroing your carbine first at 7 yards using the notch, then refining your zero at 100 yards. This way, you should at least be on paper the entire time, shortening the process overall.
I took my first carbine class several years ago at Paul Howe’s Combat Shooting and Tactics facility, and I used a carbine with iron sights only with the CSAT rear sight installed for the entirety of the class. I can attest that the sight works as designed. While everybody else was flipping to the large aperture and using offset to make accurate hits on a hostage target, I was able to simply place my sights on the target and make accurate hits at approximately 7 yards. For shooters that rely exclusively on iron sights, whether due to policy or preference, I think that the CSAT rear sight is the best option available.
For shooters that use a carbine equipped with an optic, I think familiarity with offsets and practice at close ranges may be a better option. I have tried the CSAT rear on my carbine equipped with an Aimpoint (in a lower 1/3 co-witness mount), and while it does work, I find it quicker and easier to simply maintain my normal cheek weld and offset the dot appropriately. Currently, I have the CSAT rear sight installed in a carry handle rear sight that I keep on a spare carbine, mainly to occasionally practice and keep current with iron sights.
As mentioned above, there is an alternative that may interest shooters that do use optics. My preference for folding BUIS are the sights offered by Troy Industries, and fortunately the CSAT rear is now available as an option. If your optic ever failed and you had to transition to your backup iron sights, you could employ the CSAT rear sight. Realistically, I would only try this if your optic has a quick detach mount. On my carbine that has an Aimpoint Micro T1 in a Daniel Defense fixed mount with Daniel Defense fixed BUIS, I prefer the traditional rear sight. In fact, I just recently learned that viewing the dot through a rear peep aperture can reduce the effects of astigmatism when attempting a precision shot at distance. To be fair, you could flip the CSAT rear to the traditional large notch, but I still think the CSAT rear sight is best for shooters that only have iron sights on their carbines.
In summary, I’ve used a CSAT rear sight for several years now, and I think it is a worthy upgrade to any carbine equipped with iron sights.