What is the standard for filling a shot bag? I used pebbles in mine so I didn't need to worry about the sand coming out of the bag anylonger but even this leaves some dust from the rock. BB's or things like that would cost a lot to fill 1 bag up and I never seen a tough bag to use to fill it up then insert in the shotbag to use sand again.
Marbles from a craft store? I make shot bags from old bluejeans legs, filling with gravel in a ziploc and sewing the ends shut.
But in the field, I like to use water jugs as weights because where you have people, you generally have water nearby, so just haul the empty containers and fill on location, then dump on location when you strike. Water is dense and heavy for the small volume you need. camping stores have generic-threading screw-tops with a place for attaching hooks, used for tent and tarp hold-downs.