View Full Version : Question re: sight elevation adjustment
Guys, I just received a new midlength upper. It's a flat top receiver with a 'F' marked FSB. I went to the range to zero it and I had to turn the sight post out further than any I've ever seen. I ran out of time and at that point, it was still shooting a little high at 50 yards.
The top of the post is already even with the tops of the ears. I'll need to go a little higher to get it zeroed properly. To me, this seems wrong, but I'd like to ask the experts. The post also seems to have quite a bit of slop side to side and front to rear. None of my others are like this, so I'm just wondering if it's normal in general.
Thanks!
spamsammich
10-22-08, 16:55
Silly question, but is the rear elevation drum turned fully counter-clockwise on 6/3?
There should only be a barely perceptable gap between the rear sight housing and the base.
http://i296.photobucket.com/albums/mm174/Fail2Stop/LMTRear-1.jpg
I only ask because I have seen a few shipped turned fully clockwise (large gap), and is a more common issue than I would like to admit.
Does LaRue still make a BUIS with an elevation wheel?
Silly question, but is the rear elevation drum turned fully counter-clockwise on 6/3?
There should only be a barely perceptable gap between the rear sight housing and the base.
http://i296.photobucket.com/albums/mm174/Fail2Stop/LMTRear-1.jpg
I only ask because I have seen a few shipped turned fully clockwise (large gap), and is a more common issue than I would like to admit.
This isn't an LMT BUIS, it's a Larue. But, that brings up a good point. I have an LMT BUIS and I put it on the gun today also, with the drum all the way down. With that sight, it still shot high with the front sight post out pretty far.
Failure2Stop
10-22-08, 16:59
Sorry guys, misread and deleted, but was already quoted by the time I caught my error. ;)
spamsammich
10-22-08, 16:59
If you're going for a 50 IBZ with the LMT, you'll have to adjust the wheel so you can go - (minus) 4 clicks from 6/3 to set the lowest elevation.
I should clarify. The picture that was posted looks to be of an LMT sight. I'm trying to zero with a Larue sight. I did try an LMT, and got the same result of shooting high even though I had the front sight post way out. And when I did try the LMT, it was set with it at the lowest position (for closest range).
Ok, here are a couple pics I found that illustrate the concern I have.
Here's how my front sight post typically ends up:
http://i3.photobucket.com/albums/y95/jerrellwise/Gun%20Pics/F-FSBpin.jpg
Here's how my BCM upper looks (not my actual upper, but the position of the sight post is similar):
http://i3.photobucket.com/albums/y95/jerrellwise/Gun%20Pics/StandardFSB4.jpg
So...ok or not?
spamsammich
10-23-08, 02:37
you should really take this up with bcm or whoever you bought it from first. I bet if you had, you would have had the solution by now.
you should really take this up with bcm or whoever you bought it from first. I bet if you had, you would have had the solution by now.
I'm simply trying to find out if it is a concern. I figured why bother them with something that isn't a problem?
It's a problem. I had the same with my first 16" middy from CMMG, sent it back, and they replaced it, saying the FSB was canted. It also was at/further than mil-spec on windage to zero. Contact BCM or your vendor.
spamsammich
10-23-08, 13:47
It is obviously a concern for you and a lot of us that depend on this site for info. I mention contacting the retailer first because it's a forum posting rule.
4) Contact The Manufacturer or Dealer First – Internet forums have a large global audience and unsubstantiated or ill-informed comments will affect the livelihoods of a lot of hard working people in the industry. If you have an issue with a manufacturer or dealer that you would like to resolve, we ask that your first contact them to resolve it.
BCM and his distributors are extremely helpful in resolving problems with their products. They'll get you sorted out. Without seeing pictures of your setup or handling it, this is just making you wait for answers you could have in a jiffy.
With all due respect spam, this is not a comment or claim of an issue with any specific product. It's a general question that I am asking as it relates to the AR platform. I shouldn't have posted what kind of upper I'm dealing with as it is apparently causing some confusion. I'd like to think we could ignore that and simply answer the question: Is it normal for an upper using an 'F' marked FSB to end up with the front sight post so far out that the top of it is above the sight ears? I'll go back and edit the original post to reflect this.
spamsammich
10-23-08, 15:40
Then the answer is no, not normal. And to resolve the problem I would contact the retailer or manufacturer ;) Or you could wait around for smarter men than me to answer your question.
Then the answer is no, not normal. And to resolve the problem I would contact the retailer or manufacturer ;) Or you could wait around for smarter men than me to answer your question.
That's what I'm hoping for. And why didn't you answer before? I'll certainly contact the mfg about the problem, but I'm not gonna bother the mfg with something that is normal. I hope you can understand that. I prefer to have my ducks in a row before getting the mfg or vendor involved. In fact, I'll probably try to zero it again to make sure I'm not doing something wrong.
spamsammich
10-23-08, 16:04
To be honest, I was hoping Failure2stop would have been able to help you. He has way more experience with the AR platform than I have. Sorry I can't be of more help. Is your rear BUIS moved all the way back as far as it can go?
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