+1 on the blast media. If you have a sandblasting supply anywhere close you can pick out the size you want. I picked up some cob and walnut quite a few years ago. Still haven't gone through one bag of each and it has been very good. I keep it in 5 gallon buckets until time to change it out. Alone it works good, mixed half and half it works better, throw in a couple teaspoons of Flitz and it works fantastic.
I think I paid $13 - 50# for the cob, and $18 -50# of the walnut. Never had any issues getting either out of any size cases down to .223, except when I added some Flit to a batch that already had cases in it. DUH