I just rebarrelled an M4 and noticed that with the pin on the barrel extension aligned with the slot in the threaded portion of the upper receiver that the front sight was slightly canted.

Obviously this would cause a windage misalignment.  I would like windage to be close to correct with the windage knob centered.

What are my options?  I can file the slot to be slightly over-size to remove the cant.  Can the barrel be rotated on the extension with the barrel extension fitted as-is in the receiver.  

I have seen suggestions to correct this by placing the barrel in a barrel vice followed by tapping on the carry handle with a hammer and a piece of wood... this would imply to me that its possible to turn the barrel slightly on the extenion?

Any help?

Here's what I did. I went to the Local Gun Shop and borrowed a padded set of Vice Blocks (Soft Rubber). I then took the Upper and put it in the vice about the Chamber Area or Mag Well. I put the Barrel wrench on and turned the barrel just a little and it straitened up my front sight yet still left me enough room for the Gas Tube to clear. I wouldn't do this with the Gas Tube in for obvious reasons but it was that easy. The whole thing took less than 3 minutes and my sight is as perfict as it will ever be.

Semper Fi,

It used to be only Bushmasters web site as a suggestion to fix out-of-whack windage.

Can't he try to twist the front sight on the barrel, with the barrel in a vise? If it needs it to get zeroed.