Jepp2, thanks for posting that link to Zoro. A friend and I ordered two bags and got the free shipping. Hope the 20-40 works without getting in flash holes.Agree 100%. However the shipping can be costly. I have found the cheapest place to buy it is Zoro and you get free shipping with a $50 order. I use the 20/40 sieve size as it doesn't get caught in the flash holes like the 12/20 does.
https://www.zoro.com/zoro-select-blast-media-corn-cob-20-to-40-grit-crn3-40/i/G2165387/