Did you sight yours in for 50 yards, or 100 yards? Thanks.
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My two Stag uppers (one factory built, one built by me) from August, 2006, were like this too. I measured them, and they measure about the same as the F base dimensions, and are marked with an F.
I think something must be wrong with the barrel assembly itself. The Stag built upper has the same problem as the upper built by me. I used 2 different flattop receivers (one from CMT, one from Bushmaster). Since the common denominator is the barrel assembly, I wonder if the FSB was drilled crooked (where the barrel goes through). I don't have a barrel straightness gauge, yet only have excessive elevation worries, not excessive windage worries.
Is it also possible that the bore is not centerline to the barrel? I wouldn't think so.
That's interesting. The fact that you used two different makes of receivers certainly seems to point to the barrel or FSB as likely culprits. Maybe the barrel shank which fits into the receiver isn't perfectly concentric with the barrel, or is a little off in dimensions causing it to not align properly with the receiver when installed?
I'm also sighted in at 50 yds. My front sight is so far off, I don't think any fiddling around would make a difference in my case.
A Stag owner has reported in another forum that he just received a replacement upper from Stag, and that it exhibits the same problem with the high front sight post at zero that his old one did. An acquaintance has also said that he has had two replacement uppers from Stag, with no improvement in either one. Does not bode well for the rest of us.:(
Any other S&W owners out there send your M&P15's back for repair of this sight problem? I've been without mine for going on 3 weeks now. How long did it take for yours and are you satisfied with your results?