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Optic of the Week: CSAT Folding Rear Sight

I think we are in the end of the age of iron sights. Not that they are going to suddenly go away, but more and more individuals and groups will feed no need or desire to use them in place of optics.


My dad bought a CSAT folding rear sight, and told me it didn’t work well for him. I was surprised he bought it since I was sure he perfectly happy with the ACOG/Mini Red Dot combo. I had a CSAT aperture years ago, and I liked the idea of it, but decided I’d rather put the money towards something else.

The CSAT sight was designed by Paul Howe and the intent is to have a peep sight for use at 100 yards, and a notch above for 0-7 yards.

I can’t find when I purchased the CSAT aperture I had. I think it was installed in a LMT rear sight. I did find an old note from 2009 saying that I wanted to get one, so it must have been after that. I remember shooting with it, then decided I liked the Knights Armament 2-600m rear sight better.

I didn’t know that XS Sights now makes a their own flip up rear sight. The design is similar to the Troy flip up sights, but it doesn’t look or feel as refined. It locks in the up position, and you need to press the button on the left side to lower it. The windage is easily adjustable with the knob on the right side.

I went ahead and threw the sight on one of my uppers, and gave it a try.

My dad said that when he would look though the CSAT sight, the thin bit of material between the peep and the notch would appear to disappear and it would become a giant U notch. I didn’t remember having this happen before when I had a CSAT aperture, but sure enough when I tried aiming at a wall in my home it happened to me every time.

Good in theory, but the aperture ring ghosts out & can’t be seen. It leaves you w/ a giant deep U sight picture. Not worth the cost.

Review from Midway USA.

Indoors, nose to the charging handle, this happened to me 100% of the time. If I backed my head away from the sight it became usable. Outdoors in sunlight I rarely had this issue. But it happened enough that I would never buy this sight.

The XS CSAT aperture is like an A2 aperture, but same plane. So there is a large opening and a peep that share the same zero. On this flip up sight, when you flip it up it will have the large aperture up.

If you want to use the CSAT aperture, you have to flip up the rear sight, then flip the aperture. That doesn’t make sense to me. They should have had it default to the peep+notch.

It has probably been nearly a decade since the last time I used the CSAT sight. I was dismayed to find that the notch felt HUGE. I wasn’t centering the front sight post in the notch, I was centering the entire front sight. That felt slow to me.

I had remember the CSAT as being a good sight that wasn’t for me. Using it now I thought it felt terrible. Like the notch had been made to large and interfered with the use of the peep.

When I was going to test this, I thought I would do a rough and hasty 300m zero, by zeroing a half inch low at 25 yards. Then I was going to shoot at 7 yards. I was shooting a couple of rifles, and in my haste I fired on a target I had already used. I had a really hard time trying to shoot that 3 shot group for zeroing. I couldn’t get focused on the front sight and the 3/4 inch red dot I was aiming at disappeared. The group I shot was awful.

3 shots fired with an Aimpoint PRO, note they are close together. The 3 shots with the CSAT peep were about a 2 inch group at 25 yards.

Now, normally I would say that I was shooting poorly. But I had just fired this other group with the same ammo, same distance, out of the same type of barrel using a KAC 2-600m rear sight.

3 shots, M855, 25 yards, using a 6945 and a KAC 2-600m rear sight.

The groups were shot about 5 minutes apart from each other. Shooting with the KAC sight felt easy, I was really struggling with the CSAT sight peep. After seeing how bad the group was, I made no adjustments. So I decided I wasn’t going to try and fine zero, I would instead try some faster shooting up close.

I set up up more of these dots at about 7 yards. (Thank again to the nice guy who gave me oh too very many of these red targets after he had a ton of them made for himself.)

To show the purpose of the notch, I fired some fast shots using the peep aperture of the CSAT.

Aiming directly at the red dot, I fired 5 shots of M855. You can see how the point of impact is much lower than the point of aim. The idea of the CSAT notch is so in close range situations when you need to make a precision shot, you can.

The value of the notch is being able to aim right as what you want to hit up close.

I had a handful of wolf ammo laying around, that I wanted to use up so I used it for this group. Maybe 12 or so rounds. I should have paid closer attention. The target was engaged with single shots at a moderately fast speed. Lowering the weapon between each shot. I felt really slow, as it seemed liked the whole front sight base was visible in the that notch and and I had to find the front sight post in there and line it up with the top the rear sight notch and center everything.

That would be a training and familiarity issue. More practice with the sight would lead to faster target acquisition.

If you had asked me about the CSAT aperture before last week, I would have told you it is a nice product, but something unneeded, and that something like an Aimpoint would be a far better choice on a modern fighting rifle. I wonder if they changed the design since then.

Now, having used the CSAT sight again on XS folding sight; I feel like XS flip up sight body is ok, but crude compared to others. The CSAT aperture felt terrible in use for me. I would rather use a standard A2 or detachable carry handle over it. I think I would rather use just about anything else over it.

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