Tumble-polishing sapphire is a very time consuming and expensive process.  I have done it before using the following rough guide, developed through much trial and error, that you will need to adjust to suit your quantity and size of sapphire stones.

1.  You need a rotary tumbler.  A vibratory tumbler is not aggressive enough to effectively grind sapphire.  You will need a rough grinding barrel and a finish grinding barrel.   Google "Kingsley North rotary tumblers" to see examples.  You would need the three pound tumbler for the 500g you mentioned.

2.  You need to either buy ceramic tumbling media or add more sapphire to get your barrel to 2/3 full for a proper grind. 

3. To prep the sapphire tumble them for one day with clean water filled to just above the level of the stones.  This will remove any attached iron oxides and other minerals, and also lightly round the stones.  Cleaving and chipping are to be expected from weaker stones.  Wash the barrel out and cull any stones that look like they are friable (easily chipped, will have a 'cleaved' appearance around the edges).  These will never polish properly and risk marring the final finish.

4.Tumble with 1/2 cup of ~220# silicon carbide grit for 1-2 weeks. Check the carbide in the bath to make sure it is all ground to a very fine consistency, if not then keep grinding. Your stones will be slightly more rounded but will retain their hexagonal shape. Rinse the stones completely then look for friable stones to discard.

5.  Tumble with 2/3 cup of ~600# silicon carbide grit for 1-2 weeks.  Check the carbide in the bath to make sure it is all ground to a very fine consistency, if not then keep grinding.  Your stones will be slightly more rounded but will retain their hexagonal shape.  Add ceramic tumbling media to get the barrel to 2/3 full.