Ball mill the nitrate and charcoal for at least an hour in a good mill. When a spoon full of comp will light with a match and stay lit, it is finished. The last three ingredients (listed below) are added only for ease of handling and charging into tubes. I use just the nitrate and charcoal spooned into the burrows and ignited with visco. Works well for pocket gophers and moles if you hit active burrows.
Original formula as listed in Woodchuck Control with Gas Cartridges, Dolbeer et al. http://www.aphis.usda.gov/wildlife_damage/nwrc/publications/91pubs/91-11.pdf Sodium Nitrate 58.1 Charcoal: 31.2 Mineral Oil: 5.3 Fullers earth: 4.5 Borax: 0.9