How much lead and silica sand in speaker stands?

A set of mini-pucks (good for up to 25lb speakers) at $100 is $200, vs $70 for 2 sets of the springs. Actually you will probably only need 3 springs per footer, that is you will remove 4 from each one. Then with those 4 you drill 1/4" holes into MDF, wood, acrylic or whatever, and make another two sets of springs. That's what I did. So for $70 you can do the speakers and two other components. I would hope your pucks are better than these springs. But better than the combined improvement when the leftover springs are used? Only one way to know for sure....

Sure, give em a try. The thing about all this stuff is, its pretty easy or at least predictable to say what will happen with something like what you did, mass loading. But anything beyond that- what mix, how much, etc- is pure trial and error. Including the springs. 

That's because what all this stuff is doing is controlling vibration. The springs are worth getting if only to learn about vibration control. The number of springs relative to the weight above them determines the resonant frequency of the component/spring system that in turn determines the effect on the sound that you hear. Nobsound springs make it easy to remove one or two springs and hear the difference. Stiffer is more top end less bottom end, softer is more bass less treble, and the sweet spot in between is the best of both worlds plus lower noise and greater dynamics and with less glare and a more natural sound. 

You will hear more or less similar effects changing amounts of sand and lead, but compared to how much work and mess the springs are by far the way to go. 

The pucks you have, almost certainly better than bolted. Almost anything will probably be better than bolted.

Uh oh! Bolted, you say? Sorry. While that might be fine for keeping them on the stand, its not the way to go for sound. What you want is to make the stand as inert and stable as you can, and then allow the speaker to float above it. Nobsound springs are the easiest most cost effective choice. https://www.amazon.com/Nobsound-Aluminum-Speakers-Isolation-Amplifiers/dp/B07K9ZYP84 These things are adjustable - remove springs for lighter speakers - and its crazy how good they are for the money. They are now under virtually every component in my system.

What?!?!?! What are you looking at? Filled with pure lead, sure, you got a point. But then they would be so massive you need a forklift. So how ... wait, I know this is asking A LOT ... but how about some common sense? Two bags of sand, $4 a bag (if its even 2 bags needed) plus 5lbs lead shot per stand.

Like I said, what this world is coming to.....  

Oh and to answer the question directly- fill them all the way up. As much as you can pack in there.

When I see how a simple audio question turns into a virtue signaling contest I fear for our future. I really do. 

There's two things you're trying to do here. One is add mass so the stand doesn't rock as easily. This improves dynamics and bass extension. The other is to damp the ringing of the metal. This reduces glare and harshness and improves detail.  

Packed sand will come in good contact with the metal and do a good job of damping. But its not that massive. Lead is more dense and great for adding mass but its larger and won't control the ringing as well. That's why guys combine them. Best of both worlds. 

Works even better with a little mineral oil mixed in. Use just enough to get the sand damp. Mineral oil eliminates dust and helps the sand pack better. You want it packed, not loose. Mix lead in at the same time. 

Sand mixed with mineral oil is used in my turntable rack. Both the top and bottom shelves are sand boxes. https://systems.audiogon.com/systems/8367 

This rack was built some 20+ years ago. There's lead shot on top of the phono stage. The environment is still here, and the cancer seems to be under control. Oh and I haven't electrocuted myself. Yet. 

We now return you to our regularly scheduled irrational fear-mongering.