Weird Aimpoint T1 phenomenon

Tactical Gear Optics & Mounts
1

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:

[u]*[/u]
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?

2

skew handguard and as such the front sight?

3

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

4

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

5
6

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.

7

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.

8

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.

9

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.

10

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?

11

OP: I have trouble getting ANYTHING to “lollipop” with ANY Aimpoint T1, H1, or R1 (tried all three), except for the LaRue LT103 mount and/or the LMT M16A2 style rear sight. Yes, it’s important to me for the red dot to rest on the front sight post, and since it’s my rifle, that’s how I’m going to have it. :smiley:

People tell me it’s “just me” the way I hold my head or something (technique ain’t my strong suit).

To make a long story short: try a different BUIS and you may find the problem solves itself.

It became such an aggravation to me that I use a folding rear sight now and keep it in the “down” position.

12

THIS!

When did co-witness become defined as the red dot riding atop the front sight post.

Just make sure the sights are usable through the red dot sight and your set.

Sent from my SCH-I535 using Tapatalk 2

13

Not disputing that if it works separately and he is happy then leave it alone.

But if he views the dot through the rear aperture, would be interesting to see which is dialed in. So with the red dot and rear sight both in play, shoot a group off the front sight post and group off the dot. Which is on target and which is off.

14

Because it helps to have the dot centered on the front sight post and be able to confim zero just by flipping up the BUIS and seeing if they line up…perhaps after bumping your red dot for example…and I’m talking about AFTER they have both been confirmed for POA/POI.

Yes this can still be done if the dot is off center so long as you remember exactly where the dot is supposed to be in the sight picture, but depending on where it is, it may be harder to do so vs. it being centered.

That said, I’ve never had a problem with my M3 and PRO lining up on the front sight post. I would tend to agree that it has something to do with an inconsistent cheek weld…but that’s hard to diagnose from behind a keyboard.

15

Just went into my safe and verified my t1 and m4s both line up nicely with the irons.

16

First, the idea that your dot (presuming that you’re zeroing POA/POI at the same distance on both Irons and RDS) MUST rest atop your front sight post is false.

I’ve got an H1 on an LT751, stuck on a Noveske 14.5" gun. If I get sight alignment/picture with the irons, my dot’s low and right, almost exactly like your first illustration. Irons and RDS are zeroed exactly the same and print the same, so you’d have to pay me to care less about how it LOOKS, because I’d be willing to bet my eyeteeth that all it means is that my FF forend isn’t quite perfectly true, which puts my front BUIS just a skosh out of plane with the optic. NOT substantive, as the gun shoots straight, and only one way among many that could explain a dot being somewhere besides the front sight post, yet the gun STILL being correctly co-witnessed.

Anybody thinking “I’ve never seen it NOT line up…,” that’s almost certainly completely factual: You’ve never SEEN it. One’s experience isn’t invalid…it’s the conclusion that’s jacked-up.

Second, we’re talking about non-AR-pattern guns, here. That’s gonna become important in a moment…

Third, even if the desired endstate was to achieve a certain cosmetic goal…which it’s not…, you’re assuming that the mount you’re using is meant to provide the cosmetic condition you wish in the first place. You said you’re using the Micro low mount variant. From the LaRue product description of the LT661 (emphasis mine):

No mention of co-witness, at all. Only that it mounts a Micro lower on a rail than the 660 and 660HK (each of which identify both type of guns and type of co-witness, because each of which is designed to provide for it).

Heed The Rat.

17

I don’t know if this is what is happening, but here’s a theory…

If you happen to have astigmatism, you could be zeroing the red dot based on the apparent (distorted because of your vision) center of the dot…

Looking through a peephole such as a rear sight has the effect of “correcting” astigmatism for things like a dot sight.

So if you have astigmatism you may be effectively seeing different dots depending on whether or not you are viewing through the rear sight, which could explain why you don’t get the “lollipop”.

18

This made me realize that I’ve always used a VIS upper, so it would make sense for mine to always line up. I’m about to go zero my MUR/NSR that just replaced my VIS and may very well see this happen. Like I said above though, it will still work.

19

Has anyone even looked at the gun he is having this problem?? I have no idea how tall or short his irons are. He isn’t having problems with an M4! GH

20

Far more often the dot does not perfectly sit atop the front sight post than does, in my experience and observation of a few thousand setups.

Also, since you zeroed your irons without the glass of the T1 between the sights, once you put it there you induced some degree of parallax.

I believe that both systems SHOULD be zeroed independently, as in the event of an optic failure you might need to ditch the optic and rely on the “pure” iron zero. Of course, checking POI shift through the glass with the dot off is pretty important as well.