Just got done installing a DD RIS II 12.0 FSP on my Olympic K3B-M4-A3-TC and noticed that the FSB is canted towards the right (when looking from the breech) ever so slightly.  As such the bottom panel of the RIS II rail rubs against a section of the bayonet lug.  

Interestingly enough, when I had taken the carry handle off and used it on a different upper, I had to apply about 3-4 clicks left windage whereas when the handle is installed on the Oly, the rear aperture is mechanically centered with regards to the hash marks.  I didn't think much of it until tonight when I realized that my Oly's front sight post is actually leaning right.  Makes sense to me now.

Anyway, is it worth sending the barrel and FSB back to Oly for them to somehow straighten out?  I don't see how they could do that anyway since it has already been drilled.  Perhaps they'd be willing to replace the entire barrel and FSB with another one?  If not, I might get a JP adjustable clamp on gas block FSB or one of the ARMS foldable A2 FSBs to replace the pin on unit.

On a side note, the Daniel Defense RIS II FSP rail is a very nice product albeit a pain in the ass to install.  It took me about an hour to get everything together and I would have been done sooner had I not goofed.  After removing the old FF tube and barrel nut, I installed the DD nut and locking ring then proceeded to reinstall the FSB and flash hider.  When I grabbed the top half of the DD rail, I realized that I had to remove the FSB again in order to slide the rail onto the barrel.  Apart from that, everything else went together smoothly.  I used the carry handle to line up the top rail to the receiver and then tightened the six bolts on the locking ring.  All in all, a nice product.  I like it because its overall diameter is quite smaller than the Oly FF tube and still just about as light.

I might have to get another DD FF quadrail for my BCM... good stuff.

ETA: On second thought, the gun shot straight as an arrow before so why bother...