How often to replace media in a brass cleaning tumbler

First topic message reminder :

I think it was five or six years ago that I bought a "Thumler's Tumbler" for cleaning my brass, then got a box of the cleaning media, and a bottle of Lyman "Turbo Brite" Brass Polish for Untreated Shell or Corn Cob Media.  It doesn't seem to clean my brass as well as it used to.

How often are we supposed to replace the media?  I guess I shoot a thousand or so cases a year, maybe, mostly 38 and 45.  I have a feeling I should have replaced the media long ago.

If I remember correctly, my brass used to come out shiny brass color - now it comes out looking not that much cleaner than when I put it in the tumbler.  I usually let it tumble for an hour or so - I think that's what I was advised to do a long, long time ago.

mikemyers wrote:I have no idea if 18-40 grit us what I want, and hopefully I can buy just one pound.

The numbers are for mesh size.  As in "the number of particles needed to measure an inch".  40 is okay for tumbling (very small), not sure about 18 (not sure if that is smaller than the flash hole diameter).  I use corncob for tumbling, and the mesh size is a "20-40".  Bought the stuff from an industrial supply warehouse, think 40 lbs. of it went for about $30?  (It's been a few years.)  Sold as "blasting media", it can also be found as an absorbent, and can even be used as a traction additive for icy sidewalks.  Do a websearch for it, might be surprising how many places you can find that sell it for less than $40 for a 40 lb. bag.