View Full Version : Zeroing my sights - what's normal and what isn't?
So my BCM midlength just showed up. I mounted a Daniel Defense A-1 style sight on it and set out to zero it today. Although I think I've got it pretty close now, I feel like it took way too much adjustment to get it there. My first group at 50 yards was about six inches to the right. I had enough room in the sight to get what I think will be a close enough zero to fine tune at 100 yards but my rear sight is adjusted far to the left now. I'm a little concerned that I either won't be able to get it zeroed or that if I want to try different ammunition I won't have enough room to zero with it.
So what's normal? What's in-spec and what isn't? Any insight would be appreciated.
Having to move the rear sight pretty far to the left is fairly common from my understanding. I know I had to do it for my Noveske set-up with Troy BUIS. It can be a sign of a canted FSB, but that usually isn't an issue with a quality manufacturer. My BCM is only slightly left.
As long as you're not all the way to the left and still off, I don't see much of an issue.
steelonsteel
01-12-12, 22:33
I'm sure someone like Iraqgunz will know, but it seems like it is something close to ten clicks in either direction is considered acceptable? I should dig out my old TM and find this out, I know its in there somewhere.
How many clicks from center? Do you have the Daniel Defense A1.5 Fixed Rear Sight? I think 19 clicks each direction from center is all you have. So 6 or so inches should put you about 10-12 clicks used up.
Failure2Stop
01-12-12, 22:58
The "in spec/out of spec" is based on A2 sights where the sights need to be adjustable to account for strong wind.
If that isn't your application for the weapon, as long as it can be zeroed, it's fine.
Generally, one is not going to be adjusting windage on A1 style sights under anything but range conditions.
I'm sure someone like Iraqgunz will know, but it seems like it is something close to ten clicks in either direction is considered acceptable? I should dig out my old TM and find this out, I know its in there somewhere.
It's in the end pages of the applicable milspecs but this is a midlength so I guess you could slit the difference.
From my uneducated count, it seems that I've got about 14 clicks in each direction from this sight. Right now I'm about 8 left of center at 50 yards.
With it being to the left, won't this mean that shots will continue to move laterally at longer distances?
In other words, will my shots still be on for windage at longer distances?
From my uneducated count, it seems that I've got about 14 clicks in each direction from this sight. Right now I'm about 8 left of center at 50 yards.
With it being to the left, won't this mean that shots will continue to move laterally at longer distances?
No.... If you're zeroed good at 50, you'll be fine at 100, 200, etc.
So my BCM midlength just showed up. I mounted a Daniel Defense A-1 style sight on it and set out to zero it today. Although I think I've got it pretty close now, I feel like it took way too much adjustment to get it there. My first group at 50 yards was about six inches to the right. I had enough room in the sight to get what I think will be a close enough zero to fine tune at 100 yards but my rear sight is adjusted far to the left now. I'm a little concerned that I either won't be able to get it zeroed or that if I want to try different ammunition I won't have enough room to zero with it.
So what's normal? What's in-spec and what isn't? Any insight would be appreciated.
I got a BCM 14.5 Mid-length back in Oct, had the same "problem" with a MATECH rear sight. Also noticed that the Aimpoint had to be moved considerably left of zero. Seemed a little strange but it zero'd fine and shoots great out to 200 yds. Past 200 yds there is too much operator induced error to separate any sight problems.
With it being to the left, won't this mean that shots will continue to move laterally at longer distances?
In other words, will my shots still be on for windage at longer distances?
Just as Mark said, no worries. Think about it like this. You're lining up the center-line of the sights with the center-line of the bore by moving the rear windage left and right. It's not as if the iron sights are on a different horizontal axis as the bore, and point of aim / point of impact will only cross at one lateral position. By moving the rear windage, you are eliminating that difference in axis. That's how the sights become zeroed.
Now, if your zero is imperfect, as in the difference between POA and POI, then yes, that effect and error will be magnified at longer ranges.
I recently got a BCM ltwt middy with FSP and DD A1.5 rear sight. After siting in at 50 yards, the rear sight is 13 clicks to the left, which leaves about 7 clicks left until the aperture hits the sight body. It may be slightly more or less off center and I'm not sure since the DD A1.5 rear sight doesn't have a distinct line for the center position.
The windage is fine at 100 yards. I'm not sure about 200 yards, but I can consistenly hit a 12x12 plate at about 250, so I say close enough.
I'm currently running the BCM with only irons until I can add a RDS later this month. I actually didn't notice how much offset the rear aperture was until I came across a similar thread to this one on another forum. The only potential "problem" that I can see is that once I add the RDS, the offset rear aperture may be distracting in lower 1/3 cowitness with the irons. My current setups have been absolute cowitness with flip up sights. But I'll have to wait and see when I get the RDS, but I think it'll be fine.
jonconsiglio
01-13-12, 18:50
drck1000, once you add an RDS, it'll have to be zeroed the same as the irons, so your 1/3rd cowitness will line up just fine, regardless of windage adjustment for zero.
The other month helping a friend zero a Matech rear we cranked it significantly to the left, can't remember the number of clicks, but it was quite a few. He ended up with a nice 5 shot rats nest at 25 meters and grouped fine with the junk bulk ammo at 100 meters. That said, I've got an old A.R.M.S. rear BUIS, that I have never had to adjust it more then a few clicks to get it zeroed. I don't know, maybe a combination of irons, rifle, and shooter? Now my Aimpoint in the original Aimpoint mount? Lol, that thing took me a few too many rounds to get to where I wanted it.
drck1000, once you add an RDS, it'll have to be zeroed the same as the irons, so your 1/3rd cowitness will line up just fine, regardless of windage adjustment for zero.
Yeah, I hope the RDS will align with the irons. However, i assumed that if the FSP/barrel is slightly out of alignment, if the rail on the upper is off, or if the sight body is off, then the RDS may not line up with the irons.
I understand that the RDS and irons don't need to align, but if they don't, the misalignment of the rear aperture and RDS may be distracting as I may tend to try to align the rear aperture and the FSP. I'll just have to wait and see. I also have an ARMS #40 rear sight to try out to see if the DD A1.5 rear sight is off.
jonconsiglio
01-13-12, 22:20
They'll align no matter what since the irons are lined up on you point of impact as is your RDS. So, no mater how you look at it, both have to have a point of aim that is the same in order to have the same point of impact.
The red dot moves with you and stays on target, so when you view the target through your irons, the red dot will also be visible as it too is on target.
It's no different than a mechanical zero being perfectly aligned or it needed 11 clicks of windage, the red dot will still align through the irons if both are zeroed.
I think he means the rear aperture will not be centered in the Aimpoint.
If it's cranked way over to the left, he's right, it won't be.
I had an upper that would only zero with the rear sight 2 clicks shy of all the way left. Got on my nerves and I eventually parted it out.
I'd try a different rear sight or two and if it's the upper, send it back.
jonconsiglio
01-15-12, 18:59
I think he means the rear aperture will not be centered in the Aimpoint.
If it's cranked way over to the left, he's right, it won't be.
I had an upper that would only zero with the rear sight 2 clicks shy of all the way left. Got on my nerves and I eventually parted it out.
I'd try a different rear sight or two and if it's the upper, send it back.
Ok, I just cranked my KAC rear sight all the way to the left with a T1. If I zero the T1, all three will line up, but I see what you're saying about the rear aperture itself being offset to the left of the Aimpoint.
But, how often do you actually line up all three? Also, how often do you even line them up when viewing your dot over your irons. If I take the time to center my dot in my sight picture, I'm not actually taking advantage of one of the red dot's primary features…
Now, two clicks shy of all the way left is too much. In his case, it depends on the adjustment if he'd be able to send it back since there's a standard.
The other option, if you're OCD, is to reinstall the barrel since the torque on the barrel nut can push the barrel to one side.
Failure2Stop
01-17-12, 15:23
It is not at all unusual for the dot not to sit on the tip of the FSP when both are zeroed.
Further, there is no need to combine the dot and iron sight alignment. Doing so only serves to complicate and slow the presentation.
It is not at all unusual for the dot not to sit on the tip of the FSP when both are zeroed.
I assumed it could end up with the dot not directly above the FSP, even when the irons are aligned, if any number of things are slightly off. I wasn't expecting the dot to be directly above the FSP, but I admit that I prefer if it did end up that way.
Further, there is no need to combine the dot and iron sight alignment. Doing so only serves to complicate and slow the presentation.
Just to clarify that I don't align the irons with the RDS when shooting. I have realized how much slower I am with target acquisition with irons than I am with a RDS and can't imagine how messed up I'd be if I tried to align the irons with the RDS.
Previous to my new AR, I've only had RDS absolute cowitness with flip-up irons (both front and rear). The new AR will have an Aimpoint with lower 1/3 cowitness with a fixed rear sight and FSP. I've tried shooting with the RDS and the irons up and I've found that the front sight post is distracting. Seems like my eyes sometimes focuses on the sight post because it's so close to the dot.
Coincidentally, with the absolute co-witness the dot is directly above the front sight if the irons are aligned. I guess I'll just have to wait until I have a chance to mount my RDS and just see how it turns out.
I've also discussed this with the retailer and the manufacturer and both suggested trying a different rear sight, which I have since ordered. While the offset appears to be withing specified tolerance, I just think visually I would prefer a rear aperature more centered in the sight body. Again, I'll just have to try it out and see for myself.
I think he means the rear aperture will not be centered in the Aimpoint.
If it's cranked way over to the left, he's right, it won't be.
I had an upper that would only zero with the rear sight 2 clicks shy of all the way left. Got on my nerves and I eventually parted it out.
I'd try a different rear sight or two and if it's the upper, send it back.
That's kind of what I was thinking. Again, I am not sure if that will be a distraction for me or not. . . yet. But I could see how it could be.
I've read that the natural tendency is to center the FSP post and forks in the rear aperture, granted that's when shooting with irons only. I've only used flip up irons previous to my new AR, so that was never an issue.
Ok, I just cranked my KAC rear sight all the way to the left with a T1. If I zero the T1, all three will line up, but I see what you're saying about the rear aperture itself being offset to the left of the Aimpoint.
But, how often do you actually line up all three? Also, how often do you even line them up when viewing your dot over your irons. If I take the time to center my dot in my sight picture, I'm not actually taking advantage of one of the red dot's primary features…
Now, two clicks shy of all the way left is too much. In his case, it depends on the adjustment if he'd be able to send it back since there's a standard.
The other option, if you're OCD, is to reinstall the barrel since the torque on the barrel nut can push the barrel to one side.
Yeah, I understand what you're saying. As I clarified in the previous post, I don't try to align the irons with the RDS. I just think that it may be a distraction of the natural tendency is to center the FSP in the rear aperture. I guess I'll just have to try it out and see for myself if it's truly a distraction or not.
Believe me, I totally appreciate the advantage of the RDS and it's lack of parallax. As I mentioned above, I am MUCH slower shooting with irons than RDS, as expected. It's just that I think I am way too slow with irons, but that's another subject.
Thank you very much for your insight on all of this!!! It is greatly appreciated.
http://www.brettunsvillage.com/leather/tools/garlandweightedmallets2.jpg
Submariner
01-20-12, 01:45
Just as Mark said, no worries. Think about it like this. You're lining up the center-line of the sights with the center-line of the bore by moving the rear windage left and right. It's not as if the iron sights are on a different horizontal axis as the bore, and point of aim / point of impact will only cross at one lateral position. By moving the rear windage, you are eliminating that difference in axis. That's how the sights become zeroed.
Now, if your zero is imperfect, as in the difference between POA and POI, then yes, that effect and error will be magnified at longer ranges.
How would a slight cant to the front sight base affect this?
FWIW, I did end up returning the upper for repairs.
I emailed BCM about the canted front sight base. They asked for information on how much windage I had used for my 50 yard zero so along with the response I sent a pic of my sight picture. They gave me an RA number and info on returning it. I got it back yesterday - which is less than two weeks from the time I shipped it to them. Ran a magazine through it and at 50 yards with the rear sight centered my groups are about 1" to the left so I've got plenty of windage left to use now and still have a "normal" sight picture.
It was kind of impersonal and no list of the repairs or any paperwork at all were included with the upper. But it seems to have been done correctly, it seems like the FSB is still good and solidly secured, and it's the fastest return time ever on any gun repair. I expect the repair to be fine but plan to test it a little more when the weather clears before declaring it good, but I can't really complain about their customer service at this time.
steelonsteel
01-27-12, 07:07
I wonder if they gave you a new upper? are you sure you got the old one back?
When I read the first post it sounded like I could have written it and I have kept an eye on this thread since. Now this has me wondering if my BCM middy upper has the same issue as my DD rear sight is cranked all of the way (yes all the way) to the left for zero...
The only difference between me and the OP in this instance is that I got my upper from Grant so I'm not sure who to contact to investigate further.
Cowtown556
01-27-12, 20:31
My BCM 14.5 middie was all the way to the left also, I took it apart and re installed the barrel now it is 3 clicks right. the barrel was on so tight it took a 3 foot cheater to brake the barrel nut loose. RH
I think so but I'm not 100% positive. There are a few small idiot marks on it - tiny ones that are barely noticeable. I know I'd put a few on the one I had just from handling and quick mag change practice/cycling the action. I'm not sure if the one they sent me has the same idiot marks though.
I left the sight on the upper when I sent it in for service so they could see exactly what I was dealing with. It was almost zeroed but it still bothered me. I had a couple M-16's when I was in the Army and never saw one that took that much windage to get it zeroed... so I held BCM to the same standard and was disappointed when I didn't get it. But they seem to have made good. Waiting on a break in the weather to be sure... but I think it's gonna work out OK.
I bought my rifle from Midwest Tactical and BCM serviced it with no questions asked. I'd email them directly to find out what to do and send a pic of your sight picture if possible. Their customer service is kind of impersonal... but it was fast. I think that anyone who isn't totally happy with theirs should contact them and hold them to the standard. A good company shouldn't have a problem with making repairs to get things right - especially when it's a fairly quick and easy job for a well equipped shop with some experienced gunsmiths on hand.
The hallmarks of a good company in my opinion are that they turn out a good product almost every single time and when they screw up, they fix it. So far, BCM seems to be in that category.
I wonder if they gave you a new upper? are you sure you got the old one back?
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