Tumbling media grits

So I'm looking around locally for tumbling media and some of the information I'm getting is kind of confusing/ hard to interpret. So far I've got the Lyman red Tufnut, and green corncob media. I want something more abrasive though, that will remove fine scratches or light rust. I've seen these in stores:

Walnut Shell #18-40

Abrasive bead glass #50-80, and looks like it says 150-280UM, the letters are hard to make out but the numbers are for sure.

Aluminum oxide #80

Crushed glass 20-30

I take it the crushed glass would be too harsh, but what about the aluminum oxide and bead glass? What do the numbers mean? Some type of grit rating?

I've not used it on blades but I've tumbled a lot of brass on walnut shell and on corncob and I like the results of the shell better than the cob. More $ for the shell though If I remember correctly. Been a long time.If Glen doesn't see this thread send him a PM (gssixgun) I know he uses a tumbler and he does a heck of a lot of restoring.