Filling audio rack tubes with sand, metal, grape nutz???

be carful when handling the shot fyi it is lead after all. and no idea where to buy large amounts reason I always go with pee gravel, sand or a mix of both.

you could go to a garden center and buy cleaned small pee gravel used mostly for decoration around the yard, cleaned of course as you don’t want bugs in there. the consistency is good for filling stands. another option is cleaned sand (this is what they used to put inside ashtrays for example but like one other said you will need to seal the bottom of the tubes with some clear silicon or similar. then there is the mixing fill with different constancies to help reduce any ringing-vibrations but I’ve never found it needed. I like sand for the ease of filling unfilling but you do have to seal the bottom.

I'm not a fan of using lead just not healthy for us or the environment, in this day and age there is other options better suited to your health and the health of your family.

Whatever you use, make sure you are putting it into a sealed cavity that will not spill out if tipped over and will not allow the material to escape into your home environment.  Do not ingest or inhale the material while working with it and use appropriate respiratory protection.  Both lead and silica dust are known to pose health problems if ingested or inhaled so, whatever you use, study the MSDS sheet on the material before handling.
A few thoughts come to mind;
1. Sound Anchor uses sand in their stands
2. Some people mix lead shot with the sand (like shotgun reload material)
3. Starsound Technoligies swears by their steel microbearing stuff that they used to use to damp cables
http://starsoundtechnologies.com/microBearingFill.php
4. The micro bearing stuff in #3 may be nothing more than steel blasting shot in a small fancy container - this is about a third of the cost;
https://www.google.com/shopping/product/15404022574801836148?q=small+size+Steel+shot&client=safari&sa=X&hl=en-us&biw=1024&bih=666&output=search&prmd=sinv&prds=ds:1,num:4,cs:1&tbs=vw:l,ss:44&ved=0ahUKEwjunYChyefdAhXD44MKHVqVAqYQu4UCCA8

Excellent@mitch2 just ordered a bucket of metal!

I had a friend that poured a liquid gel type compound into the legs I think he got it from one of the hobby stores. they were dead to any taping and added a surprising amount of mass. of course there is no removing at that point your committed.  

There is a product that is used to solidify latex paint for disposal. You might be able to use that with a couple quarts of inexpensive or surplus latex paint.