Just ordered a Millett DMS-1 for mine. I voted other.
Don't believe that until you try it. I have no problem with my TA31F ACOG on my XCR with stock folding tube.On the XCR the sight rail sits about 1/2" higher (in relation to the buttstock) than an AR. So I find it kind of annoying having sights that are designed for AR's on my XRC. So IMO you should rule out anything that has a lot of height built into it, like the EOtec and ACOG. These types of AR specific sights sit really high on the gun. So you are pretty much looking for a tube type optic that you can mount low. Then you just decide what range you want the optic to be suited for. I chose a IOR 4x24 M1. It's very light weight and is idea for anything 25m+ range. I would have gone with a similar tactical Leupold but I got the IOR for half the $$$. Any good 1x dot sight like the Aimpoint I consider a 100m or less optic, that is idea for urban and CQB. But to me the XCR is just a little too heavy and is certainly too accurate to use suck a short range optic.
I have tried it. I own one of the first XCR's and have tried many sights on it. I'm not saying an ACOG will not work, you will just have to have your face planted 1/2" higher on the stock to get it aligned. If you are use to a certain cheek weld, you want to maintain that on all your rifles. I also hate mounting any optics on top of an AR carry handle. Maybe I'm too picky but I think given the option most people would agree with me.Don't believe that until you try it. I have no problem with my TA31F ACOG on my XCR with stock folding tube.On the XCR the sight rail sits about 1/2" higher (in relation to the buttstock) than an AR. So I find it kind of annoying having sights that are designed for AR's on my XRC. So IMO you should rule out anything that has a lot of height built into it, like the EOtec and ACOG. These types of AR specific sights sit really high on the gun. So you are pretty much looking for a tube type optic that you can mount low. Then you just decide what range you want the optic to be suited for. I chose a IOR 4x24 M1. It's very light weight and is idea for anything 25m+ range. I would have gone with a similar tactical Leupold but I got the IOR for half the $$$. Any good 1x dot sight like the Aimpoint I consider a 100m or less optic, that is idea for urban and CQB. But to me the XCR is just a little too heavy and is certainly too accurate to use suck a short range optic.
That was the good news for me. The XCR was my first ever rifle of this type so I had no experience with cheek welds on assault/battle style rifles to overcome. The Robinson Arms websight talks about how to hold the XCR and that it's diffferent because of the narrow stock (obviously not applicable to any of the wider style stocks). My shooting with it is more akin to the flash sight picture and quick trigger pull of shooting IDPA than the deliberate taking a good breath, slowly squeezing the trigger, and having the seer release surprise you of target shooting. For me I had no problem with the ACOG. I can also understand how having the same cheek weld with a number of rifles is important and were I to replace the stock with anything it would be something like the magpul or one of the other newly announced adjustable ones.I have tried it. I own one of the first XCR's and have tried many sights on it. I'm not saying an ACOG will not work, you will just have to have your face planted 1/2" higher on the stock to get it aligned. If you are use to a certain cheek weld, you want to maintain that on all your rifles. I also hate mounting any optics on top of an AR carry handle. Maybe I'm too picky but I think given the option most people would agree with me.