Sand and shot?

Lead shot is ok, but remember it is a toxic problem, and when you discard them someday...
And filling them if you have children or pets around...
Sand on the other hand is easy to use, non toxic, easy to dispose of and works just as well.
I have B&W 501S stands filled with sand and they are great.
Remember to dry the sand, then pack it down by vibrating or tapping the stands to settle and pack the dry sand as much as possible before sealing them.

Lead shot has greater mass per volume than sand and mass is what is desired when filling stands. Sure lead is toxic if handled all the time, but inside your stands poses no danger to you, your kids or pets. Some folks like to mix sand in with the lead to fill the gaps, but lead is soft and doesn't vibrate, so sand isn't really needed.

When you buy your sand go to Lowe's or similar store that stocks it on shelves INSIDE the store. This should guarantee that it is dry. Buy the fine grade. A couple of weeks ago I got some like this at Lowe's to fill a new pair of Dynaudio Stand 4's. It worked great.