I have been using porous ceramic granules for the past four years as my cleaner of choice when the cases are real dirty or to remove black powder fouling in my Lyman 1200 and RCBS unit with no problems to the tumblers. I have access to these montmorillonite granules ranging in size from 2.15 mm down as small 0.20 mm. The smaller sizes work well because they go through the flash hole. 
I tumble the cases until I clean off the heavy dirt [maybe 15 minutes] and finish with corn cob for the final polishing. At the Labor Day match I gave samples to one off the Michigan black powder cartridge shooters to try.
The materials are light weight [about 34 pounds per cubic foot].

Pilgram

gents,
have been using a dillon for the past 3 years with ceramic, and have not had the slightest problem wit erosion or wear. they are hdpe and take a lot of punishment. also found that after about 3 hours they are done.
irish