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.

This post comes up every few months! Lead shot is best, the smaller the pellets [higher #'s of bird-shot], the more dense the pack.

Some cautions...as Elizabeth mentioned, lead can have toxic effects, and needs to be disposed of properly [recycling or giving to a gun store]. Rinse the new shot pellets a few times in a bucket to remove the dust. WEAR A DUST PROTECTION MASK WHILE DOING THIS!!! And don't worry about pouring the water down the drain, but DO NOT pour the rinse water into the ground. When the shot dries, CAREFULLY pour it into the stand filler holes, and then seal the stand up. Use a funnel, if necessary, and be sure to inspect and remove any and every pellet that has fallen onto the floor. You're all set...no worries.

Children are very susceptible to lead poisoning. The method of exposure primarily involves eating lead paint chips, which supposedly have a sweet flavor. Lead paint is no longer available to the consumer market, but it still does have industrial applications. Inhalation of lead dust or vapor is also very dangerous. Again, interior house paint used to contain lead, so you just can't sand it down and repaint! It involves a HazMat removal, which can cost several thousand dollars...or more!

Also, it requires a prolonged and repeated exposure [inhalation or ingestion] for toxicity, but the effects can be permanent. It's a material where small non repetitive exposures is nowhere near as dangerous as the media hype portrays.