Sights acting weird.

[26 Inf]

The OP said he had a BCM upper. No further info.

Clyde 777 -

Was the Aimpoint new, or did you move it from another rifle?

When you zeroed the Aimpoint did you have to move it much for windage?

Have you shot the Aimpoint on another rifle?

If so, was it on for windage?

If you haven't shot the Aimpoint on the other rifle, do so and advise where it is hitting. If it hits pretty much on then I would say that you have a problem with the BUIS or how they are mounted.

Since you said that you used the sights on another rifle and they centered what I'm wondering is if the rail on your hand guard is aligned square with the rail on the receiver.

There are several ways to check this, the easiest way is if you have an electronic level, simply place the reciever onto a lower receiver vise block. Lay the level across the upper's rail and look at the reading, then do the same on the rail section your front sight is mounted on. Compare readings. Mine reads in tenths of a degree.

On the rifle I checked, the receiver was 2.9 and the rail just behind the front sight was 3.1, Which means two tenths of a degree difference. Apparently either my vice or my homemade vise pads are 2.9 to degrees off level. Just for kicks I also used a bubble level. I really couldn't see any difference which leads me to believe if you can see appreciable difference on a bubble level, you've got problems.

Anyways, I would work from there.....

[Failure2Stop]

Yeah no shit but thats at the extreme end.

So?
The adjustment range associated with open sights in the past was correlated to wind adjustments at 500 yards with no other sighting devices, with a front sight that was mechanically attached to the barrel.
If you need to spin additional wind at the edge of iron sight range then I'd say you might want to find another solution. If not, I'd recommend leaving it alone and focusing on the stuff that really matters to your use.
Whatever you want is what matters, but if it doesn't affect that, I don't think it's worth worrying about.

[Rifleman_04]

My DDM4V7 requires the rear sight to be almost all the way to the left. It's just the way it is.

When did something so unacceptable become so accepted?

[Rifleman_04]

This is why sights are adjustable...

Within certain limits for a zero.

[AKDoug]

When did something so unacceptable become so accepted?

Combining a light weight tube handguard with with a removable DD front sight, and a Matech folding rear sight and you will have some degree of error. I could start messing with centering the handguard, or I could just go shoot. It works fine as is, especially since it is a backup.

We discussed this a few years back and found that the U.S. Military no longer has a spec for centering the rear sight. It just has to be able to be zeroed.

[kirkland]

Another reason why I like lower 1/3. No need to worry about iron sights cowitnessing with red dot or whatever.

[seb5]

Another reason why I like lower 1/3. No need to worry about iron sights cowitnessing with red dot or whatever.

I agree but it won't impact the windage on the BUIS either way. I've always preferred the lower 1/3 but many don't. Just a hmmm thing but we recently got 15 Aimpoints through DLA (used to be DRMO) and I noticed that 11 of them were set up without the spacer, so were absolute co witness.

[Iraqgunz]

I am still waiting to hear which BCM upper we are discussing.

[Hkbeltfed]

The two sighting systems have independent zeroes. Or at least they should, when done correctly.

If they were sighted for the same distance, why would they?

[jackblack73]

If they were sighted for the same distance, why would they?

That comment and the comments about co-witnessing have confused me. If an optic is parallax free, and most red dot type sights are, or very close, then if sighted at the same distance shouldn’t they co-witness, even if no attempt was made to co-witness?