If My FSB Is Not Canted, Help Me Figure Out What's Going On!

[HKUSP.40]

Question for you guys....On both my LMT fixed rear BUIS and my Troy flip up rear BUIS, my windage has to be set 15-20 clicks to the left to be zeroed. My first thought was canted FSB. I have a brand new factory fresh BCM carbine so I hoped that wasn't the case. Before I emailed them and sent my upper in...I took some pics and determined that a canted FSB is likely not the reason. Take a look:

http://img820.imageshack.us/img820/1181/bcmfsp.jpg

Judging by that pic, the FSP is nearly dead center. I used the gridlines on the camera so everything is level and proportionate. Maybe it's the way I'm aiming? I am cross-eye dominant (right handed pistol shooter but with left eye). However, I shoot my rifle left handed. I still have quite a bit of room to go with the windage so it's not maxed out but it just bugs me. Any thoughts/opinions/ideas? Or should I just leave it be and be happy?

[bsmith_shoot]

Hey brother, ive been there before. Ive got a 11.5" BCM that I thought was canted also, but it wasnt. I had to adjust my DD1.5 sight really far to the left to get zero. I decided to shave the fsp and throw on a C4 10" rail, ans figured I would go with Troy flips on the front and rear. Before the switch, I mounted the rear and zeroed it. It was about 15 clicks to the left.
I went ahead and done the shave job and mounted the rail, threw on the sights and zeroed. It was still about 10 clicks left. I checked the rail for cant, and it was perfect almost. I looked down the rail at the fsb, and there was great clearance.
I cant explain why the sights have to be adjusted that far, but it happens. I wouldnt worry about it, just adjust and shoot it.
Brandon

[3 AE]

I'll keep this simple. Can you hit what you're aiming at? If yes, than ride on. You stated that you have plenty of adjustment left. Just because it's not perfectly dead center in the windage adjustment range does NOT mean there is a problem.

[Iraqgunz]

Why do you assume that 15-20 clicks is somehow excessive? You are worried about nothing.

[HKUSP.40]

Fair enough. It just sparked my curiosity more than anything. I've seen anywhere from 6-13 clicks is "within spec" but either way I appreciate the insight/opinions.

[GTifosi]

Not cranked over so far that it gets bound against the side of the body is within the functional range of the rear sight.

[fixit69]

I've had the same problem with Troy flip ups. But I like the look of the sight.

Just adjust your windage to where your hiting the target and not slamed to one side or the other. If you take them off, it will probably change again. That's been my experience with them and other flip ups.

[Sticks]

Front sight post/pin not centered?

Try rotating it one one way or the other in elevation first by 90* then 180* from initial setting and see if that changes anything.

[tpelle]

On a 20" rifle, 0.006" offset of the front sight post (or the rear aperture) is equal to 1" at 100 yards. (0.006" is roughly the diameter of a human hair.)

For a shorter sight radius, as on a shorter barrel, it will take less offset of the rear sight to get that 1" POI shift. Conversely, the same degree of offset will result in a larger POI shift.

I have an A2 set up as an NRA Highpower Rifle competition rifle. In that game you shoot iron sights, and at ranges of 200, 300, and 600 yards. You need to be able to adjust the rear sight to try to compensate for wind shifts, so you want to have your "no wind zero" with the rear sight centered up, just so you have the maximum range of adjustment to either side. As a result, most of these rifles are equipped with a front sight tower that is held in place with setscrews on each side that bear against flats milled in the barrel. Trying to get a zero with one of these can be tough, as hardly any tweaking of the setscrews results in major POI shifts, and you end up chasing your shots all over the target (and beyond). To sight one of these in, after you shoot a group and do the arithmetic to determine how much you need to move the front sight, you clamp the dial indicator to the barrel and zero it against the front sight, then adjust the setscrews to appropriate amount. Then you LocTite the snot out of it so it doesn't move.

For "social" situations, however, you will likely never move the rear sight windage after you sight in. So if you can zero, you probably are good to go.