There's something about this thread that just isn't up to snuff when measuring it with my snuffometer.
The vagueness of the OP's question is being met with entirely too specific answers.
It's like someone asking, "I'm working on my car, what size wrench should I use?"
Only to be met confidently with answers such as, "Definitely a 53/64ths. Without a doubt."
First of all, I've never lubed anything I've ever cast with silicone.
Second of all, the only thing that needs to be lubed when casting is the mould, not the bullets, as the bullets would be made out of molten lead, therefore extremely hard to lubricate.
I usually lube my bullets before loading them, not when casting them. Although, I have tried setting the still hot bullets in wax to lube them, but this was a real PITA, so I went back to tumble lubing them. I usually use bullet lube such as liquid alox, although I've experimented with parafin and several types of wax.
As far as lubing my moulds, I simply use carbon straight from a burning match. I've yet to find anything that works better.
Or are you talking about flux?
Otherwise, this may be an excellent opportunity for an old dog to learn new tricks. After all, if we always did things the way we always have, we'd still be flying canvas airplanes and sailing wooden boats. So my curiosity is piqued, and I'd be very interested in learning how the heck I could use silicone, and what the heck Id use it for when casting other than to spray it on the bearings of the fan I use for ventilation.