I use a 3/8 granite ..here they call it rice stone, as long as it's not rounded (pee stone is NO good ) it has to lock into each other.
Stone dust is another, I use to get it from Home Crapo, in bags, it will splash up onto the tracks...
Take a sample of the stone dust home ( 5 gallon ) and make a test trench and lay some track and see how it holds up.
I have used it, it will splash up onto the track initially causing you to clean the track ..some mix it 50/50 with Type III bond glue .
This forms a shell like thing ..it can be hit with a hammer to break up, after a soaking..
Horay !
Well done .. Well done ..
Hopefully the track will just lay down and not fight ya !
Great work ... I can't wait for the train video's ... I use You-tube and Vimeo ( I like Vimeo a little better )