Sound advice from Jerry right there . I use heaps of stag antler but here in Australia we have plenty of different species to try . We have Red deer , Fallow, Chital , Russa , Hog , Elk , some Sika and of course the mighty Sambar. I have used them all except the Sika. Some have more of the spongy pith than others , the most solid is Russa and Sambar. To keep the most pattern possible on the finished knife split the straightest pieces down the middle with the band saw. flatten them a bit on the belt grinder and then put your full tang handle on the inside of the scale. Draw around it and then profile the outer edge of the stag down to the pencil line. you will probably then have a white boarder that could be from a couple of mm to six mm thick , depending on the overall thickness of the stag. You can then grind the white inside surface down to where the white outer boarder disappears or the stag reaches your preferred thickness. Then glue and pin as you would on a normal handle material. If you are using Red deer or Elk you can hollow out the spongy pith and fill it with epoxy then process it as above.
If your doing partial tangs drill out the spongy pith and replace it with a good solid epoxy then drill scrape out and process as you would a piece of Micarta or wood. Obviously the bigger and thicker the better for slab handles and then you look for the popcorn pattern and good color if you can get it .