I loaded 20 577/450 cartridges with 38 gr. IMR 4198 and used Puff-Lon as a filler. It appears to be a fine sawdust impregnated with graphite or molybdenum as it leaves a dark smudge on the fingers. I followed the instrructions on the container and tamped the filler over the powder to the neck and then to the mouth of the case followed by seating the 405 gr. boolit. Shot 12-14" high at 100 yds, and the cases had a sweet burnt-wood smell after firing.