Okay to use a wire-brush on angle grinder to remove rust? I found this old hammer head and I'm trying to restore it. I've had some luck removing the rust with 40 grit sandpaper and a sander but I'm going to need to get into those grooves and though that a wire brush on an angle grinder might be faster.
The objective is to remove the rust. What would work best in this scenario? And how do I remove the rust from inside the handle hole?
I'd use my drill-mounted wire brushes on the outside.  I've got a range of shapes and the slower, speed-controlled drill would be gentler on the workpiece.
For the inside, I think you'll have to do it by hand.  Steel wool wrapped round a dowel, or better a piece of 2x1 planed down to to an oval that fits freely inside the hole, should do the trick.  If you use enough steel wool you can wrap it onto the end of your stick and staple/nail it in place