M249 with Eotech. My personal primary carry for a while
The Eotech is a parallax free, battery operated reflex sight. While I had my doubts about the speed benefits of reflex sights, it is undeniable that they work well and it is undeniable that the Eotech is an excellent sight (when working) for rapid shooting at <100m and an acceptable out beyond that to about 200m. But they do have their share of issues.
You can read some general info on reflex sights if you are interested.
Eotech has over 13 models that all more or less do the same thing. They come in the XP series (newer) and the older, 500 series.
(Eotech 512, 516, 517, 552, 553, 556)
The only difference between these models is simply the type of battery they use, how well it supports night vision and if the brightness/NV buttons are mounted on the side or rear.
Standard 65MOA, 1 MOA Eotech reticle
They all have 2 batteries, mounted in line with the barrel and the standard 65MOA/1MOA reticle.
Before I explain the issues with the 500 series, let me say that most people can buy a 500 series sight and live a long life without ever having a problem.
However, while a great sight to use, they suffer from some fundamental design errors. If you take a given hundred of any model, you are going to have issues with several of them. Firstly, the batteries are in line with the barrel, which makes them in line with the recoil. That is not a problem generally or on other sights, but the as battery case is longer than the batteries, the extra space is taken up by 2 rubber grommets with a wire spring in them to complete the connection.
Sometimes recoil can make batteries bounce a little inside the case, making the reticle disappear for a split second every time you fire. It is awful. Additionally, the grommets can simply fall out while changing batteries, or stick to the batteries when you take them out and fall off later. If you lose one, you have to improvise (soft hearing protection and a wire works ok) or you have no sight.
These little grommets have caused a lot of guys a lot of headaches and stress
The awful grommet issue has been mostly corrected and you can now get after-market support that does the same job with 1 piece and better rubber. But you need to keep an eye out for it.
Battery life is another issue. For AA batteries it is measured in days, not months or years like some alternative sights (Aimpoint). Yes, you get warning by the reticle flashing, but all the same, having a sight that will die in less than a couple weeks of regular use is not ideal.
As fast as the batteries die, they would die much faster if Eotech did not use an ingenious technique of utilizing an inert gas (I think nitrogen) to make the reticle appear brighter for the same amount of power. Much like lasers that use gas for the same purpose.
However, the gas can leak and it leaks a lot faster if you leave cheap batteries in the sight, which are prone to leaking a small amount of acid which starts work immediately on the wall in the sight that holds the gas in. Once the gas is gone, the reticle is so dim it washes out completely in bright daylight.
But how likely is it that any of this crap I am talking about will happen you may ask? Well, in a batch of over 100 Eotech 552’s, I have seen over 10% fail due to acid leak/gas loss and I have seen at least 50 grommets go missing in less than year. Not to mention a least 1 daily failure due to grommet/battery connection issues that could be resolved by just working with it.
Despite all that, if you can pick one up for $400 or less, I still recommend you get one. However, they are far from being an idiot proof sight. Change the grommets to the newer, one piece style and have back up iron sights.
(Eotech EXPS2, XPS2, XPS2, XPS3 and XPS2 RF [RF=Rim Fire=cheaper and weaker] )
They all take a CR123 battery mounted sideways. The idea being to eliminate the blinking that can be caused by the recoil being in line with the batteries. They also say they improved the gas issue and fixed all other complaints with the 500 series. And, for the most part they did a great job of taking the cons out of the older series. Battery life is better, but still far from an Aimpont.
A few new reticles are offered, but I don’t advise getting them. The old reticle is just as versatile with a little practice, and easier to use with less practice.
As with all illuminated reticles, night vision is not some high speed switch to an IR sight. It is simply a very dim normal reticle. I have yet to use an Eotech of either series that you could not use with night vision just by dimming the sight as far as it goes.