I still don't use a vice. I just hold the horn and work on it. Arms, legs and fat belly is all I need
A few tips for when you get started. If you're going to cut octagon flats on the horn tip. Draw lines where the edges will be. That's in the book. But what helps is if you sight strait down the tip, if the lines are crooked it will be more visible looking at it that way. Draw them in pencil first in case you need to erase and adjust.
to get the flats really flat with good sharp edges, first make the flats with rasp and file but then finish them up by scrapeing them with a curved blade pocket knife. That will make the flats slightly concave, not enough to see but enough to make sure they aren't rounded over and it makes nice sharp edges.
When antiquing, after the rit dye you can put potassium permanganate ('Old Bones') solution on it. It mellows out the color of the rit dye, makes it look more natural I think. PotPerm is not light fast permanent though unfortunately.
When putting a wire coathanger inside to find the depth of the hollow of the horn, lay the wire along the side of the horn, not the inside curve or the outside curve. It's more accurate that way. If you measure on the inside curve and then on the outside curve it can be as much as an inch difference.
The book will have you draw a line to follow for the drill bit when you're drilling the hole in the tip. It's good to use 2 lines 90degrees apart, keeps the drill going straight in two dimensions rather than just one. Drill out the side one time and you'll know what I mean.
Well that's a few things I figured out along the way, hope it helps.