New to red dot optics - Eotech XPS2-0 questions

[ra2bach]

No FSB - MBUS front and rear on a 12" C4 rail... Unless the C4 rail is canted... I don't see that happening from BCM though - you never know...

actually it was a topic of a thread where several people mentioned their BCM front sight being canted. it happened to me so no one is immune.

to be fair, it's been a while and none of these were outside of the adjustability of the rear sight but to say it doesn't happen with any one particular manufacturer is not correct...

[ra2bach]

Yeah, I mean with a regular cheek weld, it came from the factory looking like the reticle was hanging over the rail. It wasn't parallax or anything. I mean, from just about any angle that you looked through it, it was faaaaaaaar right. I don't need to shoot it to know that it was off. The laser boresight seemed to confirm it. I boresighted the MBUS and the XPS separately, and then they co-witnessed perfectly, but the MBUS windage is way far left. I was just trying to get some insight so that maybe I can save some ammo at the range getting it zeroed.

ah, that doesn't seem right. if you are looking at the reticle, not through the rear sight, it is possible for it to appear to be in any quadrant of the optic window while still being on target.

however, if you are lining it up with your iron sights, and they are zeroed, and the reticle still appears off center, then something's wrong...

[Shao]

ah, that doesn't seem right. if you are looking at the reticle, not through the rear sight, it is possible for it to appear to be in any quadrant of the optic window while still being on target.

however, if you are lining it up with your iron sights, and they are zeroed, and the reticle still appears off center, then something's wrong...

Maybe I wasn't clear - it was far off to the right from the factory, but I did a preliminary alignment using a laser boresight, then did the same with my BUIS (which weren't zeroed - it was unfired and just built at the time I started this thread). After doing so, my absolute co-witness was perfect - but my MBUS rear was over to the left further than I thought it should have been.

Windage for the iron sights "way far left" is usually associated with some canting of your FSB, which in turn is usually due the barrel turning a little within the Limits f the index pin when torquing down the barrel nut. Not uncommon. It has nothing to do with the Eotech, of course.

Whoa... So should I return the upper to BCM or is there an easy fix for that I can do from home?

Anyway - UPDATE: I took it to the range yesterday and it pretty much shot POA from the get go using irons and the Eotech. So I'm still confused as ever. I checked the alignment of the receiver rail and the C4 rail and it looks perfect... I don't get it...

[SapperRob]

Maybe I wasn't clear - it was far off to the right from the factory, but I did a preliminary alignment using a laser boresight, then did the same with my BUIS (which weren't zeroed - it was unfired and just built at the time I started this thread). After doing so, my absolute co-witness was perfect - but my MBUS rear was over to the left further than I thought it should have been.



Whoa... So should I return the upper to BCM or is there an easy fix for that I can do from home?

Anyway - UPDATE: I took it to the range yesterday and it pretty much shot POA from the get go using irons and the Eotech. So I'm still confused as ever. I checked the alignment of the receiver rail and the C4 rail and it looks perfect... I don't get it...

What is not to get? You were able to zero both your irons and optic within factory specs. A rifle with perfectly centered irons is the exception to the rule. And like you said, I have never, ever had any optic "centered" new in the box. Sometimes you're lucky if you are even on paper out of the box....

Just go shoot and don't sweat things not being "perfect".

Rob

[Shao]

Fair enough... I guess too many years of shooting with fixed sights have screwed with my head. It just doesn't look right...

I also just realized that I completely missed what Hmac was getting at... As stated earlier, no FSB...

Anyway, I'm going to swap out the MBUS rear with a Troy that I have and if I need to adjust the windage in the same way, I'll stop worrying about it.