View Full Version : Lower 1/3 Zero and Irons
Quick question.
Im mounting a T1 in a lower 3rd mount and I wanted to get a ruff zero.
I know you can zero off your irons if you co witness but I was wondering if anyone has a method of doing it with a higher mount.
I think it would also be useful to do a good zero check in a field expedient manner.
Any ideas?
Quick question.
Im mounting a T1 in a lower 3rd mount and I wanted to get a ruff zero.
I know you can zero off your irons if you co witness but I was wondering if anyone has a method of doing it with a higher mount.
I think it would also be useful to do a good zero check in a field expedient manner.
Any ideas?
The T-1 is a parallax free optic, so yes, you can basically mount it, and zero it to your pre-zeroed irons. The lower 1/3 co-witness has nothing to do with it due to the lack of parallax. However, you definitely need to get to the range and fine tune the dot at whatever range you want to be zeroed for before any serious use.
Quick question.
Im mounting a T1 in a lower 3rd mount and I wanted to get a ruff zero.
I know you can zero off your irons if you co witness but I was wondering if anyone has a method of doing it with a higher mount.
I think it would also be useful to do a good zero check in a field expedient manner.
Any ideas?
I've done that. I have a T-1 with the Larue high QD mount. I ran my gun with just irons for a while before getting the T-1. I had the irons zeroed at 50 yards and after I mounted the T-1, I did a rough zero of the T-1 at 50 yards by holding the POA of the irons and adjusting the red dot to match. I did have to fine tune it a little bit to tweak the POI after that process, but it wasn't much.
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If you can see your BUIS's through the T-1, you can co-witness the RDS. It doesn't matter, on the height, as long as you can see both the F & R sights in the field of view. The T-1 is parallax-free enough to get you pretty close even at the extreme edges of the FOV.
FWIW, you probably know this, but the 1/3 Co-Witness mount for a RDS is taller than the Absolute Co-Witness height.
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Doc Glockster
04-04-12, 14:06
Okay, just for clarification, isn't a 1/3 co-witness meant for those who want to use the red dot without looking through the irons? If you plan to zero the dot through the iron sight picture aren't you better off with an absolute co-witness? With a 1/3 co-witness isn't the idea that you look over the top of the rear sight loop when using the dot, and if the dot goes down you simply lower your head and look through the irons and through the empty RDS window?
Or do I have it all wrong?
Okay, just for clarification, isn't a 1/3 co-witness meant for those who want to use the red dot without looking through the irons? If you plan to zero the dot through the iron sight picture aren't you better off with an absolute co-witness? With a 1/3 co-witness isn't the idea that you look over the top of the rear sight loop when using the dot, and if the dot goes down you simply lower your head and look through the irons and through the empty RDS window?
Or do I have it all wrong?
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From what I understand, the purpose of 1/3 Co-Witness is to keep the BUIS sight picture at the bottom of the FOV in the RDS, so you can raise your head slightly and have the RDS in the center of the FOV above the BUIS's.
I think the 1/3 Co-Witness is more suited for having the BUIS up and ready to go than Absolute Co-Witness.
But maybe it's just me...
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Okay, just for clarification, isn't a 1/3 co-witness meant for those who want to use the red dot without looking through the irons? If you plan to zero the dot through the iron sight picture aren't you better off with an absolute co-witness? With a 1/3 co-witness isn't the idea that you look over the top of the rear sight loop when using the dot, and if the dot goes down you simply lower your head and look through the irons and through the empty RDS window?
Or do I have it all wrong?
Someone can correct me if I am wrong, but since the T1 is parallax free (as least beyond really close range) it does not matter where in the FOV the dot is when you zero it. It is best if it is in the center but you can get it close looking through the lower 1/3 then fine tuning while centering the dot. That is one of the great things about these optics, as long as you can see the dot and put it on the target, you should be able to get hits.
Doc Glockster
04-04-12, 15:16
Someone can correct me if I am wrong, but since the T1 is parallax free (as least beyond really close range) it does not matter where in the FOV the dot is when you zero it. It is best if it is in the center but you can get it close looking through the lower 1/3 then fine tuning while centering the dot. That is one of the great things about these optics, as long as you can see the dot and put it on the target, you should be able to get hits.
I realize that, but I thought the purpose of a 1/3 co-witness was to allow you to look through the RDS without looking through the irons?
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FWIW, you probably know this, but the 1/3 Co-Witness mount for a RDS is taller than the Absolute Co-Witness height.
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Say what? It's not the other way around? :confused:
You guys are making this way harder than it needs to be. Check this out:
http://i52.tinypic.com/15wh1es.jpg
There's also a whole stickied thread on co-witness in the optics forum, which is where this thread should be to begin with.
The lack of parallax in the T-1 sight makes it possible to accurately view the dot anywhere in the T-1's window.
The lower 1/3 refers to the T-1 being raised to a height such that the irons appear in the lower 1/3 of the T-1's viewing window when centering your eye on the T-1's window.
If you press down into viewing through the irons, and the T-1 and irons are both zeroed for the same distance, you will see the T-1's dot on top of your front sight post. The point is, you can use this version of a co-witnessed sight picture for a quick zero-check on the T-1. However, it is not a replacement for actually zeroing the optic at the desired range.
Deleted....ASH556 and I had the same traffic.
Doc Glockster
04-04-12, 15:38
So with the 1/3 co-witness you still expect to line up the dot with the front sight post?
Then why have a 1/3 co-witness? I thought the purpose of a 1/3 co-witness was so you could use either the RDS or the irons (without having to line up both) if you wished? In other words, it lets you have a fixed rear BUIS that is also out of the way when you're not using it, right?
If you're going to line up all three as in the third pic, then why not have an absolute co-witness?
It's not logical to use a 1/3 co-witness if you are still going to try to line up the dot with the irons all the time.
:blink:
EDITED TO ADD: Okay, it looks like you can use it either way. The center pic is the one I'd opt for unless the red dot goes down. Then I'd look through it like the third pic.
This is why I gave up and went with a folding rear BUIS. I never could get everything lined up with a 1/3 co-witness.
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There was a guy at the range the other night that was saying a RDS was too complicated trying to line the Dot up with the BUIS.
I explained that when the RDS and the BUIS are sighted in, you should just ignore the BUIS and use the RDS. He was using his BUIS and RDS at the same time...whew!!! Just because the RDS and BUIS can Co-Witness, doesn't mean you use them that way all of the time??
The purpose of 1/3 Co-Witness is to have the Dot in the center of the FOV while the BUIS's are down low, not obstructing the majority of the FOV....but ready to go, with a slight head shift, if needed.
If you're not sure your RDS is on target, just look through your BUIS and the Dot should be on the tip of the Front Sight. Then, if all is well, ignore the BUIS and use the Dot, you're gtg.
YMMV
...at least, this is how it works for me.
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Failure2Stop
04-04-12, 16:59
If you're going to line up all three as in the third pic, then why not have an absolute co-witness?
If you are taking the time to line up all three parts of two sighting systems you are doing it wrong.
Doc Glockster
04-04-12, 17:31
If you're not sure your RDS is on target, just look through your BUIS and the Dot should be on the tip of the Front Sight.
This never worked for me. Something is always off-center.
If you are taking the time to line up all three parts of two sighting systems you are doing it wrong.
I'm slowly learning this, hard-headed as I am. :D
I finally let myself feel guilty about having a cheapo GG&G fold-up BUIS on my carbine, and installed the fixed Daniel Defense 1.5 rear sight instead.
It's going to take some getting used to, but it's not too difficult to use the RDS over the BUIS and then lower my head to sight through the irons if the RDS goes down. The visual clutter isn't as bad as a full co-witness.
Dang, I might actually get used to this tactical shit after all. :help:
This never worked for me. Something is always off-center.
Probably a head position issue with the irons. That's why the dot is off-center. Either that, or something's not zeroed properly. Have you had quality carbine instruction? As LAV has said, 30 min with a hands-on trainer will explain and fix what would take days on the internet.
Doc Glockster
04-04-12, 17:41
Probably a head position issue with the irons. That's why the dot is off-center.
I wear glasses and most people laugh at my head position. I tend to hold my head back and that's just the way it is. That's why I despise a gun like the AK because your face is right at the receiver cover, and why I prefer a tall mount for my T-1. Truth be told, I probably couldn't "unlearn" my stance very easily. After more than 20 years of shooting, though, it's comfortable for me and I have done reasonably well in competitions.
Either that, or something's not zeroed properly. Have you had quality carbine instruction? As LAV has said, 30 min with a hands-on trainer will explain and fix what would take days on the internet.
I had law enforcement range training/time, but nuthin' fancy.
I hit purty near every thing I aim at. :D
There's a guy at every gun show offering CCW training, and every time I stop and ask about carbine training. All I ever hear is "someday."
Hey thanks for the responses guys. I haven't really had a chance to read them all over, my wife's got a stomach bug an I'm chasing a 9 month old around.
I didn't want you guys thinking I didn't appreciate the input.
This never worked for me. Something is always off-center.
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There are a lot of variables for everything to line up perfectly; such as: head position, sight cant, old eyes, blah, blah, blah.
When I'm Co-Witnessing, the Dot isn't perfectly top dead centered on the FS post, it is more like on the right side on the top of the post, still very close.
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You guys are making this way harder than it needs to be. Check this out:
http://i52.tinypic.com/15wh1es.jpg
There's also a whole stickied thread on co-witness in the optics forum, which is where this thread should be to begin with.
The lack of parallax in the T-1 sight makes it possible to accurately view the dot anywhere in the T-1's window.
The lower 1/3 refers to the T-1 being raised to a height such that the irons appear in the lower 1/3 of the T-1's viewing window when centering your eye on the T-1's window.
If you press down into viewing through the irons, and the T-1 and irons are both zeroed for the same distance, you will see the T-1's dot on top of your front sight post. The point is, you can use this version of a co-witnessed sight picture for a quick zero-check on the T-1. However, it is not a replacement for actually zeroing the optic at the desired range.
Oh, duh, I get it now. Of course the mount for the optic is higher. :o
Thanks for the edumacatin'.
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