I know this topic has been posted before for Stag uppers, but I’ve got a S&W M&P15 (made by Stag) with the same problem, and I was curious if there are any M&P15 owners here who have contacted S&W about this and what their response was. I’ll probably call them on Monday, but would like as much info from other owners as possible beforehand.
Again, this problem involves having to set the front sight post so high that the top of the post sticks up above the level of the protective “ears” of the FSB when attempting to zero the elevation of the M4 carbine. This problem seems to be isolated to owners of Stags and S&W’s. A friend of mine who owns a Bushmaster M4 type does not have this problem. Several people have mentioned having this problem when using the ARMS#40 backup rear sight(including me), but I reinstalled the original carry handle rear sight and am having the same problem with that, so it doesn’t appear to be a sight problem.
Some people, including me, also have a problem with having to move the rear sight aperture way to the right in order to zero the windage on these rifles.
There is also a discussion about this problem in another forum:
If you don’t have a F stamped front sight base, then your front sight post will look like it’s going to fall out. Bushmaster sells a .030" taller front sight post for $5.50 that will cure this.
Here’s some pics I found on another website showing the difference of a F FSB and a standard one.
This is what I used on my flat top upper without the “F” front sight base. Without this I had the same issue that you described above. Quick and easy fix and this is a well documented issue with flat top receivers and carry handles.
I just measured my S&W front sight base. It is marked with the F and matches the measurements shown above for an F base. While I don’t know when it was made I traded for it new in the box back in November. Perhaps this is a recent problem?
[b]My front sight base is marked with the “F”. I did order the taller front sight post from Bushmaster and installed it, but the problem with it and the original is that the top of the post sticks up above the level of the protective “ears” of the FSB and is therefore exposed to possible damage if I drop it or bang it against something. This defeats the purpose of the protective “ears”. I tend to agree with others who say that there is a manufacturing flaw with these uppers made by Stag, probably with a limited batch. If they are mil spec, I don’t think they should be this way. A friend with a Bushmaster M4 and the ARMS #40 rear sight does not have this problem. His front sight post is well below the top of the protective “ears”.
Here’s my S&W front sight: [/b]
And my Colt front sight:
I believe that the top of the front sight post should be sitting about where it is in the photo of the Colt when it is zeroed properly, not where it is in the photo of the S&W. A taller front sight post will not solve this problem. The top of the post is where you place the target and it will always be there whether a taller front sight post is used or not. Since my front sight base is an “F” and appears to be the proper height, I have to assume that the problem is that the barrel is slightly canted upward, or there is a problem with the receiver, or some other problem. Anyway, I’m calling S&W because this is unacceptable to me, considering how much I paid for this carbine.
Does the top of your front sight post also stick way up above the top of the protective"ears", and your rear sight aperture sit far to the right side of the rear sight base when your iron sights are zeroed?
No, but it is pretty close. Looking at your photos my post does not set nearly as high. I’m not experienced enough to pass judgement on what might cause this. I also saw several posts about windage problems but I have not experienced that. Mine is pretty much centered once zeroed.
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 sighted in at 50 yds. I’m trying something I read about sighting at 50 and it being on at 200 yards. I still need to fire at 200 yds to finetune as well as doublecheck the zero. We’ll see then.
[b]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. [/b]
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?
[/b]