Weird Aimpoint T1 phenomenon

[G19A3]

I apologize in advance for what must seem like a newbie question.

I have two genuine Aimpoint T1's. They are not really close in serial numbers, so reducing the possibility of manufacturing defects in the same production lot. They were purchased a few years ago from Botach (I know, but I never had problems with them). They are both mounted on separate FN FS2000s with Larue QD low mounts. The optics are positioned as far forward on the rail as possible. In fact, they are right behind the front sight wings.

They both have the same problem, they will NOT co-witness. The iron sights are in the lower third of the T1. This is lowest QD mount that allows any possible co-witness.

My procedure is: I FIRST sight in the weapons at 50 yards with no optics . . . only iron BUIS (Mounted correctly, so they are not the variable). Nice repeatable groups.

SECOND, I attach the T1 via Larue mount to the rail (T1 to Larue mount attached correctly and blue thread locked). BUIS are folded out of the way. I sight in the red dot at the same target at 50 yards. Again, nice repeatable groups.

When done, I flip up the rear BUIS and shoulder the rifle. The red dot is NOT on top NOR centered over the front iron sight. The dot is low, entirely below the horizontal top edge of the front sight post and off to the right, slightly overlapping the right edge of the post.

I hope I can illustrate what I see:
_
l l*
l l
l l

The asterisk represents the red dot as viewed through the BUIS on both T1's.

It should be like this:

*
l l
l l
l l



I thought it very odd as every co-witness pic I have seen shows the red dot sitting centered on the top of the front sight. As I do not shoot with the BUIS raised, it has not been a concern all this time. I figured I would QD the optic if it ever went tits up and then flip up the BUIS. But this doesn't seem ideal.

After everything was sighted in as detailed above, I decided to get cute and mess with it. I adjusted the elevation and windage of the red dot so it did co-witness, centered on top of the front iron sight. This time....a nice group appeared approx. 1.5" low and right. Crap!

In other words, my BUIS are shooting to different points of impact depending whether I sight in with the BUIS alone compared to sighting in the BUIS while looking through the T1. This is with two different rifles with identical set ups.

It does this with different ammo (55gr, 62gr, 75gr). I have decent vision and do not wear eyeglasses, though I may be ever slightly far-sighted.

Am I reversing the co-witness procedure? For example, is the proper procedure to first mount the T1 on the rail and then sight in both iron BUIS and red dot? If this is the case, I would think the optic cannot be detached as the optic's distortion is required to accurately shoot your BUIS. What happens if the glass cracked or fogged to the point you have to detach the T1?

Is it due to the extreme forward mounting? Is it my eyes?

[Lian]

skew handguard and as such the front sight?

[Iraqgunz]

I am not following at all. Which mount do you have? Larue absolute co-witness, lower 1/3 co-witness or the short?

[G19A3]

I am not following at all. Which mount do you have? Larue absolute co-witness, lower 1/3 co-witness or the short?

My English composition-fu is weak. I edited my original post in an attempt to clarify.

[DTakas]

- - - - -

[The Rat]

You're overthinking it a bit. As long as you are on target with the irons by themselves, and with the Micro by itself, then you are good to go. Whether or not the dot lollipops on the front sight is irrelevant. The dot shouldn't interact with the irons other than that initial rough cowitness to get you on paper, but that's just a starting point. You have to fold the irons down and zero it properly from there.

[Chameleox]

They both have the same problem, they will NOT co-witness. The iron sights are in the lower third of the T1. This is lowest QD mount that allows any possible co-witness.

If you're using a lower 1/3 co-witness, they will not likely align. If you're dialed in with your optic by itself, and with your irons by themselves, you're good to go.

[dmaxfireman]

You're overthinking it a bit. As long as you are on target with the irons by themselves, and with the Micro by itself, then you are good to go. Whether or not the dot lollipops on the front sight is irrelevant. The dot shouldn't interact with the irons other than that initial rough cowitness to get you on paper, but that's just a starting point. You have to fold the irons down and zero it properly from there.

Gotta disagree with this, you should be lined up vertically. Horizontally is all dependent on the zero distance
.

My first guess is that there is a inconsistent cheek weld. If you were to use your BUIS and red dot at the same time which has the more centered group.

[DreadPirateMoyer]

I believe you're using an absolute cowitness, not a lower 1/3rd?

And on that note, I've never had an Aimpoint and BUIS line up perfectly when individually zeroed, and I also use absolute cowitness mounts.

Is your rear sight zeroed to the right? I've noticed that the dot often tracks to the right or left on the front sight post respective to the right or left adjustment on the rear sight.

This has always bothered me, but I've confirmed zero with my sights multiple times, so I think it's fine. It makes sense to me, at least from an engineering perspective, because unless the sights are PRECISELY mounted on the same vertical and horizontal plane (which is almost impossible), I can't see their sight picture/zero lining up perfectly anyway. I'm honestly not sure if that's even possible.

[The Rat]

Gotta disagree with this, you should be lined up vertically. Horizontally is all dependent on the zero distance
.

What difference does it make?

If my irons hit POA/POI at my chosen zero distance, then they're good to go.

Likewise if my red dot hits POA/POI at my chosen zero distance, it is good to go as well.

Why mess with it past that?