The easiest is to go to a Pet Store and buy Bird Cage sand, alternatively Play Pit sand is also good and fine. One thing you must do after that Sunday Roast is put the sand in the oven on a tray to make sure it is thoroughly dry. It’s then easier to put into the sand bag. Use a small funnel that fits into the leader leather tube or as I did make up a thin cardboard one stuck together with cellotape. I since found that my Reloading Powder funnel will fit perfectly, make sure you clean it before loading any more centre fire cartridges. There is what they call a ‘Heavy Sand’ available but I only know of Sinclair in the US as a supplier.