Dremel bit?

[Flinty Scot]

I find a warded (no teeth on one o more sides) file most useful for this sort of adjustment.
For widening a rear sight, you probably want one with warded edges, so you don't accidentally deepen it as you widen it, and vice versa.

 

[billraby]

If you want to use power tools, get a Foredom flex shaft machine. Two big differences. First the motor is separate from the hand piece. You are holding a tool that weighs only a few ounces and is much smaller. You have far more control. Also it is controlled by a foot pedal. You can run it very slow if you need to. Yes, a Foredom is expensive. But when you wreck a $500 stock blank that you already have 100 hours of work into I can promise that you will wish that YOU HAD JUST USED THE RIGHT TOOL IN THE FIRST PLACE!!!

 

[Elkeater]

I bought a fine toothed hack saw blade. I'll use files for final tune. Now I have to get to the range. Snow again this morning.

 

[pilot]

"Sneak up on it" The best advice for working on gun sights. A dremel doesn't sneak up on anything.