Steel (sp.gr. 7.8)
Various alloys available (low carbon, high carbon, chrome steel, stainless steel, etc.) in a variety of forms:
Ball bearings Good wear, very round but will result in metallic contamination. Cost directly related to material and inversely proportional to size. 1/16″ to 6″.
Shot Irregular shapes with lumps and bumps, but only cost effective alternative for steel in sizes less than 1mm. Inexpensive, sizes from 90 microns to 3mm.
Other forms Steel wire can be cut and formed to produce diagonals, ballcones (looks like a flattened ice cream cone), pins (rods), oval balls and other shapes.