All this talk about sphere size, density and actual size of BBs reminds me of an old physics experiment that has to do with filling a given space.
The teacher places a container on the table and box of rocks. He pours the rocks into the container to the top and asks the class if I it is full. The class says yes.
The teacher then takes a box of pebbles and proceeds to pour them over the rocks in the same container, and then asks the class if the container is full. Of course they say yes.
The teacher then takes a box of sand and pours the sand into the same container that has already been filled twice, once with rocks and again with rocks and pebbles. He asks the class if the container is full and they say yes.
The teacher asks again and the class confirms the container is full it cannot hold any more, where upon the teacher takes a glass of water and pours it into the container until the water reaches the top.
So let’s review: rocks followed by pebbles, followed by sand, followed by water. Each time the container is filled even thought it was thought to be full.
The lesson, start with BBs, then pour in lead shot, followed by tungsten dust. The fill the voids with liquid, ie glue.
Or do what I do, purchase a box of stick on weights from the local tire dealer. They come in both ¼ and ½ oz sizes and are easy to cut into even smaller size. Far cheaper.