For front sights, a hacksaw, small chisel and triangular file will suffice.
For rear sights:
What you want by chiseling the dovetail is to raise a lump on either side of the sight so that you can form it and file it to shape.
To make the pocket, I cut down with a hacksaw, cuts as close together as I can, which leaves a little web of metal sticking up between cuts. Use a new blade. Watch the depth of cut carefully. One deep line makes all the others have to come to that level. Then I take a small chisel, and chip the fins down to the floor level. Then the area gets filed flat and true.
At this point I use a big cold chisel, driving into the little vertical wall on either end of the cut down dovetail area. I pound a little, then look to see if the chisel started right. if not started right, like the chisel is hitting too high on the wall, file with a triangle file to flatten out the very inside corner. then reset the chisel and pound some more.
I end up filing the pocket anyway, so I don't worry about the chisel being EXACTLY at the right angle, or exactly square to the barrel.
If you raise too much metal, it can be filed off. This chiseling of the sight lumps is really a cold forging operation. you can tap it back down, or shape it a bit with the hammer and punch to get the effect you want.
this lump was raised only on the back of the pocket because of the extension on the front of the sight.