I never filed a front sight like you described there. The ones I have filed I use an straight file with fine teeth. I also take a chunk of milk carton, make a slit in it the size of the sight, and put that over the sight. That protects your barrel from file slips. The other thing I do is use white out. I paint the top of the sight and then file that white ... off. I then go shoot the rifle and see how much more I need to take off.