Hi! I’m new here but have had AR’s for many years. This is the first time I’ve run into this but this is my first and only carbine with a BUIS.
I sighted in this new upper today and had to move the windage pretty far to the left. My other AR’s are a Colt A2, a Nodak receiver Retro M16A1 clone and a Compass Lake service rifle. All are within a couple of clicks of center.
Here is a pic. What do you guys think?
t
No, that is perfectly fine. As long as you can get a zero, and still have more adjustment to go, IMO it is perfectly acceptable to have the sight adjusted off center.
Who made the upper? Or, if it’s a build, who made the barrel and pinned the FSB?
What you’re seeing is well within the norm for mass produced and pinned FSB’s. It’s kinda irritating but, it’s within spec.
Hit the search function and you’ll find other threads on this same subject.
I hit the “Orange” Search button and typed in “excessive windage”. The result was this.
You’ll be able to find your answer within those results.
Of course it helps when you provide us more details about the weapon.
Whoo Hoo! Gold mine of info there… That’ll keep me busy reading for a while…
A company built the upper but but I didn’t want to bust their chops without giving then a chance to fix it if it turned out to be way off. The barrel is FN but I’m sure the company puts the FSB on and assembles the rest.
It was 17 clicks left of center. I’m assuming that Magpul’s are 1MOA clicks.
t
Iraqgunz… Its an M4 carbine clone built with an FN MP CL 1/7 5.56 barrel. F marked front sight base pinned. A2 flash. Magpul Gen 2 MBUS rear. Colt M16 BCG. I’ve got it on my Compass Lake Engineering built A2 service rifle lower with the CLE NM trigger to test it for function and sighting in.
t
I would get another rear sight and see if it does the same thing.
Yep…and try reinstalling the one you have. It’s easier than folks want to realize to have one not get squared down properly on the rail.
But at the end of the day, that adjustment is there for a reason… 
Those are great points … I have a friend that has a Stag with removable carry handle. I’ll try and grab that and see if its changes things. I’ll also remove and reinstall this MBUS and maybe move it up a spot on the rail to see if that changes it too.
Yep, I had a Troy Rear sight (expensive) that was canted and did that. The worse thing was I sent it back, and they immediately sent me a replacement one that did exactly the same thing…I guess it was good customer service, but received 2 bad products.
I wound up just dremeling the second sight to correct the cant.
I’ve got the same problem with one of my rifles. Daniel Defense barrel, F marked FSB and I’ve used Magpul gen 1 and Troy BUIS. Even the Aimpoint R-1 lines up with the sights with the excessive windage.
PK Firearms built it and offered to take a look at it and fix it but I just never sent it in. Other uppers I’ve gotten from them have been great.
Place a level across a flat on the upper receiver and see if the rear sight assembly appears canted to the right when the receiver is level. If it is canted, you have found the problem. Try a carry handle off another AR-15 and see if you still have to adjust the sight the same amount to the left to zero. If you do, the front sight is probably canted to the left and you will have to find someone with the tools to reindex the barrel.
I was told by a major AR manufacture that 13 clicks from mechanical zero on the rear sight is acceptable. I do not find it acceptable and make adjustments until I am within 2 clicks of mechanical zero on the rear sight. I like to have the extra windage adjustment available to make corrections when I am shooting at distance on a windy day.
Good luck and let us know how it turns out.
I am pretty sure 13 is well within any spec and I know for a fact that I have had Colts that were 13 and maybe more. I would be concerned if I was hitting the side of the sight.
Here is a pic with levels on both the rail and the Magpul base
Does the front sight assembly appear canted to the left when the rifle is level? It does not take much cant to cause what you are describing. Try throwing a level across the front sight wings and see what it looks like.
i did that just that. I used the level in the foreground and bubble splits the right mark on the level. I thought one wing could be higher than the other.
I would suggest putting a different rear sight on the rifle and see if it requires so much left windage. A full carry handle type sight is preferred to check. If the rifle shoots close to mechanical zero on the rear windage with the carry handle, I would throw the sight in the photo back on the rifle and run with it. It won’t cause you any problems unless you are shooting at distances of 300-400 yards or farther and have a need to compensate for a strong left to right wind.
It took 17 clicks left of center to zero it at 50 yrds. I’m going to borrow a carry handle and see what happens.
+1. That’s what I would do