View Full Version : DD Rear BUIS dialed all the way to the left when zeroed.
Just installed a Daniel Defense fixed rear BUIS on a Colt 6920. It it behind an Aimpoint T-1 and fixed front sight. It is mounted on a LT tall mount so it the iron sights are in the lower 1/3rd of the T-1. When I zero the iron sights at 100 yards I have to dial the rear sight almost all the way to the left side of the housing. When I turn on the T-1 and look through the iron sights, the red dot IS co-witnessed with front sight in the lower 1/3rd of the optic, as I would expect. However, with the rear sight dialed all the way to the left, it seems like the alignment of the iron sight is diagonal across the top of the rifle. I expected that the iron sights and the red dot would be more generally in line with the center of the rifle. Anyone seen anything similar?
Right now I have an EOTech mounted on one of those RRA "Dominator" risers (don't laugh, it was FREE) with the built-in rear sight. Mine isn't drifted ALL the way to the left, but I had to move it over a significant amount.
I'm looking to get rid of that mount and put a normal BUIS like an MBUS or Troy on there, and I'm curious to see if it will be the same. To me that would imply the rail isn't perfectly in line with the bore. This is on a BCM upper.
Its funny that this is brought up because I emailed someone about it a few weeks ago. I was at a carbine class and 4 out of 12 rifles had the rear buis dialed all the way to the left. It really threw me for a loop since they were made by well known and respected manufacturers and I could be wrong, but it would seem to be an alignment issue. No wind that day.
My interest in this all started with me having a colt carbine upper with a larue rail that I purchased used; once it was zero'd it too was all all the way to the left, and I mean it wouldnt go any further... It bugged me so much, I sold it. I tried a couple diff. buis brands, and it was still that way. For ref: I was using a 100 yd. zero.
Im interested to know the technical variables of this as well.
No problems with my DD A1.5 rear and I've had it on since they came out.
Did you buy this sight new or used? Any noticeable defects with either the rifle or sight (noticeable cant)? Did you try removing and remounting?
Is this the first iron sight you've had on the rifle? If not what was the situation with the previous? If it is the first try a different rear if possible to help determine if the issue is with the sight or the rifle. If another rear iron sight zero's normally contact DD and they will take care of you.
I've never heard of an issue like this with this sight.
Good luck!
Just installed a Daniel Defense fixed rear BUIS on a Colt 6920. It it behind an Aimpoint T-1 and fixed front sight. It is mounted on a LT tall mount so it the iron sights are in the lower 1/3rd of the T-1. When I zero the iron sights at 100 yards I have to dial the rear sight almost all the way to the left side of the housing. When I turn on the T-1 and look through the iron sights, the red dot IS co-witnessed with front sight in the lower 1/3rd of the optic, as I would expect. However, with the rear sight dialed all the way to the left, it seems like the alignment of the iron sight is diagonal across the top of the rifle. I expected that the iron sights and the red dot would be more generally in line with the center of the rifle. Anyone seen anything similar?
First, let's cover some facts. Your rear ap can be somewhere around 12 clicks in either direction and still be "in spec."
With that said, the reason for large adjustment in windage is generally due to your FSB being off center. The other reason for this is that the rear sight is not mounted on the receiver properly OR the is receiver is not square and true (rare that this is the cause).
Have you or anyone else ever removed the FSB from the barrel and then re-installed it?
C4
The farther the rear sight is from the center, the more I'd be wondering about my front sight. If an FSP is canted to the side, that will cause headaches in getting the rear sight windage dialed in. If there is no FSP and the front sight is mounted on a rail, it usually means the rail is crooked.
I suppose it could be that the barrel is crooked, but that would be farther down the list on a quality rifle.
Funny this comes up. I have 5 different DD A1.5's on my rifles. 4 of them zero near center of the sight, and one, is WAY to the left of center, but I am able to obtain a zero. This sight is attached to an upper with a DD 16" LW mid barrel. It bugged me so much, I swapped uppers with another I had on hand, thinking this may help. When taking it all apart, and the optic and rear buis off, I really eyeballed how everyting lines up. It was obvious that the FSB is canted to the left. Argh. I go ahead and swap upper, and yep, when eyeballing it, it is still the FSB, canted, with this upper too. No fixing that, but I guess its not that big of a deal, since I can actually obtain a zero with it. Its just irritating, everytime I look down those sights. :(
Really interesting replies and experiences. It is sort of weirdly comforting that I'm not alone in this experience. The rifle is basically new. I've had it for a couple of years but have only put a limited number of rounds through it. I have never done anything to it other that remove the handle and install the T-1 (which came with the LT high base attached) and DD BUIS; and those were basically just screwed on the factory rail. I am intrigued about the thoughts on the FSB. I wonder if it is out of alignment. I would think it has to be either that, or the rail. It is very interesting that this has happened to others with some regularity. I'm going to give it all a workout in a Larry Vickers carbine class this weekend in Carthage, NC so I'll see if I can get a chance to ask LAV if he has any thoughts.
ghostman1960
03-03-11, 20:59
Its funny that this is brought up because I emailed someone about it a few weeks ago. I was at a carbine class and 4 out of 12 rifles had the rear buis dialed all the way to the left. It really threw me for a loop since they were made by well known and respected manufacturers and I could be wrong, but it would seem to be an alignment issue. No wind that day.
My interest in this all started with me having a colt carbine upper with a larue rail that I purchased used; once it was zero'd it too was all all the way to the left, and I mean it wouldnt go any further... It bugged me so much, I sold it. I tried a couple diff. buis brands, and it was still that way. For ref: I was using a 100 yd. zero.
Im interested to know the technical variables of this as well.
Canted FSB.
Duplicate post has been deleted
It's not the rear sights fault, you either got a canted front sight post or the barrel is off.
I got a Spikes middy upper on trade and the rear sight needed to be adjusted left. (about center of full left and center) I called spikes and they said send it in , Gave me a call tag via e-mail in an hour for free shipping and didn't care I got it used.
I figured they would just wack the front sight post over but they sent me a BRAND NEW upper with new Bolt , CG and charging handle. SONOFABIOCH! It came back tested dead on with my sight attached.
Good look with Colt doing that. :fie: But give them a call anyway.
I had this issue with my 6720 I recently picked up. I had to run the rear sight all the way to the left just to center it at 25 yards. Colt sent a shipping tag for it and fixed it. I just got it back last week and it shoots fine now. As far as I'm concerned, Colt has great customer service. Give them a call - I'm sure they'll treat you as good as they did me.
Barrel is not aligned properly in the receiver. It needs to be removed and reinstalled.
Barrel is not aligned properly in the receiver. It needs to be removed and reinstalled.
You're saying that you think there's too much slop in the indexing pin and the barrel got rotated to the left too much when the barrel nut was torqued down?
Barrel is not aligned properly in the receiver. It needs to be removed and reinstalled.
I will second Hmac's comment. I am not the OP, but did post in this thread, about the same issue, and mine being caused by a canted FSB. In my case, it is not an issue of barrel index. I tried two different upper receivers on this barrel, and both had normal sized index slots, with the normal, very tiny amount of clearance around the index pin. I have put together many, many uppers, and in fact, have never seen an index pin slot in an upper receiver, that would allow the barrel to rotate in the receiver far enough, to make the FSB as canted as the one on my particular case. On my barrel, the index pin on the barrel extension, is not inline with the FSB. I suspect this is the OP's problem as well.
You're saying that you think there's too much slop in the indexing pin and the barrel got rotated to the left too much when the barrel nut was torqued down?
Not to much slop... The clearance between the index pin and the index slot in the receiver is not a slip fit. There is an allowable tolerance. When the barrel nut is torqued, it moves the index pin against the left side of the index slot. The index pin needs to be centered in the index slot.
If the FSB was installed correctly at the factory, there is nothing that can be done to fix the problem unless you are willing to apply a fat roll of cash to the problem.
The DD fixed BUIS may be the culprit also.
LOL. I bought a set of DD A1.5's from a private seller and when they arrived, the rear was adjusted all the way left as well. :D
And i was worried that mine was 4 clicks left of center....
Ironically, my red dot was out of the box centered.... Not a single adjustment required.
This conversation sounds real familiar? Didn't we discuss this recently?
Barrel is not aligned properly in the receiver. It needs to be removed and reinstalled.
ColdDeadHands
03-04-11, 18:41
My fixed troy rear sight's aperture needed a bit of adjustment too to get it zeroed. It is at the 2nd dash to the left. This is on a BCM Upper, never been messed with. In hind sight I guess the 2nd dash isn't too bad...
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