Rice hulls are commonly specified as a medium for making burst charge for smaller diameter shells. (3" and under) The problem I have is there aren't too many rice processors here in Indiana.  I can mail order 50 lbs but then I have to find a place to store them and keep the insects out.  One thing that is easily obtained just about anywhere is grass seed so that's what I went with.

I start by soaking my seed in water for around 20 minutes. You can try misting your seed and stirring but I found soaking to be much easier.

After the seeds have soaked, I simply cover the container with a towel, grip it tightly, and swing it around to get the excess water out. The dog thinks this is great fun and waits for me to let go of the cup.

Dump your dampened seeds into a suitable container with a lid. Here, I'm using a peanut butter container. I find that Potato Salad containers work well too.

Start adding your fast meal powder with 5% Dextrin or better yet, 2-3% SGRS, added. While some people call for a ratio of 5-7 parts meal to 1 part carrier, I don't seem to be able to go past 4-5 parts without additional wetting. I add about 1/3 of my meal, put the lid on, and shake vigorously. Repeat until the seed won't take any more meal. If necessary, you can spray the mix and add more meal.

Now, it's simply a matter of spreading the burst on plastic and letting it dry. I occasionally stir the pile to break up lumps and speed up the drying. Once its dry (2-3 hours in the sun), I sift out the fine powder that didn't stick and save it for later. The powder can be used  the next time or used as a prime on fuse.

Actually, just about anything readily available that absorbs a little water can be used. Other mediums used with good reports are ground corn cob, vermiculite, wood shavings, etc. Find something lightweight and give it a try.