C4 rail, and alignment issues?

[bsmith_shoot]

I recently done a fsp chop, and threw on a 10" C4 rail on my BCM 11.5. I was bore sighting my rifle, and noticed that the chopped fsp was almost touching the inside of my rail. I inspected the rail to reciever mating, and everything seemed fine. When I was bore sighting my Troy sights, I didnt have to move my sights a single click, they were spot on. My T1, when mounted in my LaRue tall mount, was only about 4 clicks high. Whats the problem here? Im going to shoot it some tomorrow, and see if there is cant to the rail, but acording to the laser bore sight, they are perfect. Any ideas?

[bsmith_shoot]

It was only close on one side. It was obviously off center.

[seb5]

I've installed 4 of the Centurion rails. The first one did this. After tinkering with it for 30 minutes or so I realized that you need to make sure you alternate tightening the screws each half turn or so. Kind of like tightening lug nuts. If you don't evenly tighten you can end up with the torque pulling the rail to one side or the other. The good news it's an easy fix.

[J_Dub_503]

Sen5 hit it on the head...it's extremely important to use a star pattern when tightening any screws.

[Robb Jensen]

Your shaved FSB could be just thicker on one side. Or it could be not straight on your barrel.

[bsmith_shoot]

Your shaved FSB could be just thicker on one side.

That was my first thought Rob, but upon closer inspection, my rail was canted. I loosened the screws, leveled it up, then tightened it properly. Looks perfect. Im gonna take the calipers to it tomorrow, and see how close it is. The boresighter showed it was still good, so im happy with my job. Ill never buy another built upper again. Ill build my own from now on.
Thanks a bunch guys.
God bless,
Brandon