Read through my posts in this thread
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Read through my posts in this thread
Please don't ever link this site to the folks over there.:D
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I built an AR using a Sabre 16" barrel with a CMT flat top M4 upper. I had the same problem, I had to correct for windage almost all the way left on my BUIS. I thought the FSB was canted, but it turned out the upper reciever was faulty. I took the thing apart many times trying to correct the problem before I realized what was really wrong. I sanded a little off the tab in the upper so I could spin the barrel a little, that corrected the sight but my M4 feedramps didn't line up properly and I could see that my FSB was now canted. I finally gave up after a year of tinkering and bought a whole new upper reciever. Guess what the new one lined up perfectly and I didn't have to put more than a few clicks of adjustment on my BUIS.
I sent my old upper back to CMT with a letter explaining what was wrong with the thing. I didn't call them, I just sent the thing back. A couple weeks later I got a brand new reciever in the mail. And now that reciever turned into a new gun:)
So it may be a long shot but make sure your upper is not faulty before you start pounding on your FSB. If your FSB is canted you should be able to tell by eyeballing it with your Foward handgaurd installed. If it looks straight up while you are looking down your handgaurd you could have a not so flat, flat top.
I bought an upper which takes several more than 21 rear clicks to the left. I purchased it without BCG or BUIS, but the vendor wants those sent...(option "a")...is that logical, or should the canting be able to be remedied without needing those?
So I'm thinking about (b) calling around town for a knowledgable gunsmith (probably cost more than shipping, but would keep it local), or...
(c) smacking it myself with a rubber mallet, since that's what Grant says most guys do anyhow. If you'd advise me to try that, what do you clamp in the vice, the upper receiver?
ETA: I found the other thread on this: https://www.m4carbine.net/archive/in...p/t-18088.html ...So I think I'll try "C."
pertinent quotes: C4IGrant08-19-2008, 08:43 AM (in reply to: That wouldn't damage the upper receiver?)
"No. Just as an FYI, this is how all manufacturers get FSB's straight. ;)"
C4
"I have the upper secured and then simply hit the FSB to the left or right (depending on which way it needs to be moved)."