I have a RRA flat top rifle and with Troy buis on the rear and the standard front sight.  I noticed the rifle needs excessive windage to zero.. I think the front standard sight is canted to the right a hair.....Is there a way to true the sight?

What do you consider excessive windage? Usually like 10-12 clicks is considered in spec.

Quoted: I have a RRA flat top rifle and with Troy buis on the rear and the standard front sight.  I noticed the rifle needs excessive windage to zero.. I think the front standard sight is canted to the right a hair.....Is there a way to true the sight?

You true the front sight by rotating the entire barrel in the upper receiver barrel socket to get the sights in index with the bore plane (including barrel harmonics).

One way to correctly index the FSB to the needed index is to reinstall the barrel with the front sight/barrel indexed the needed amount (read takes too long and a few tries before reaching perfection),

The other preferred way is to hold onto the upper receiver only very tightly, then use a leather mallet to make blows on the base of the FSB just above the barrel to slip the entire barrel in the upper receiver barrel socket the needed rotation/index.  If your good, it takes about ten test rounds, and about four blows to have the rear sight set dead center with the FSB rotated just right for a true zero.

isnt there an indexing pin on the barrel that fits into the reciever? WOuldnt you damage the reciever if you pound on the sight and barrel trying to rotate it?

Also wouldnt the barrel nut have to ideally be retightened?

The barrel extension pin fits into a slot in the upper receiver barrel socket (read there is some slop, and chances are, the pin was pinned over to the one side when the barrel was tighten). Even if the slot was beyound tight on the pin, the pin will slighty indent into the side (read if you where to pull the barrel to correct, you would still need to correct the problem with a file, and use shims to hold the barrel in the correct index as you retightened the barrel nut).

The only tension that the barrel nuts puts on the barrel/extension to the upper receiver is surfaces tension.  Trust me, it going to take a few healthy blows to slip the barrel even a few degrees, and as long as the barrel nut was tightened correctly from the start (read greater than 35, but less than 80 lbs), the barrel nut will still be tight.

Bottom line is the choice of either drifting the barrel in the socket using a leather mallet, or pulling the barrel and playing the lets find the correct index under live fire, then re-adjusting with a few more barrel pulls, is yours. But, let me put it this way, you take the rifle to any AR smith, and your going to find that the handle on his leather mallet still warm as he comes out of the back room and hand the rifle back to you after correcting the problem.