Anti-vibration balls for hifi racks

No matter what you use make sure it is dry. Any moisture and it will rust the inside and it would be a pain down the road.  If you go with steel balls or buckshot there is another option of shot peening material.  Steel shot for treating metal at sand blasting facilities.  It wears out and gets tossed.  Many different sizes although much smaller diameter than buckshot.  The used material should be almost free.  You could buy new of course buy I'm unsure of the current cost. Good luck John

You could use steel shot instead of lead. Steel shot is used for waterfowl hunting to reduce environmental pollution. 

Sounds like good ideas, steel shot. 

A friend of mine was a DJ, he told me that they would put turntables on top of bicycle inner tubes, stretched across some wooden frames.  Hundreds of people dancing, and the turntables did not skip.

I guess I am a fan of isolation, rather than adding mass. 

I have a turntable hung from the ceiling, in my "man cave", off of long springs. It never skips. Looks cool too.

Kiln Dried Sand is the substance required. 

In the days of old, some would suggest a mixture of grain sizes was the best formula for Sand Fill. 

The Science for Kiln Dried Sand is that each grain is independent, and Kinetic Energy will attempt to transfer into each grain, resulting in energy transferal dissipating efficiently. 

The Frame for the Rack must be recognised to have a ring when Kinetic Energy is present. 

Sand seems like a good and inexpensive solution. I have no personal experience with following product, but it is marketed for this purpose: Atacama Atabite SMD-Z 7HD Inert Filler. I imagine there are others.