I would like to walnut shells as my blast media, but so far what I have gotten is too coarse to go through the blast guns that I have (one from Harbor Freight and the other from Eastwood). Mostly working to remove rust and scale blasting in the gravel driveway in front of the workshop. I see coal slag and aluminum oxide along with glass beads in finer grits. Soda seems to be for paint, not rust. Any opinions on what media to use, the health and environmental concerns of them are welcome. Thanks!

Steve