Glen,
Think about this.
If you have lube left in the grooves, that means that all the forces you mentioned didn't do their job at pumping lube what so ever. So where was the seal? And where did the lube go?
If lube were liquefied it would flow under those conditions. In the summer, more would be used up and the winter you would find more on the bullets. That's how my handgun stuff is. So why is that? Same load. Same rotational and acceleration forces. Just less heat to melt my lube is why. Rifles I never find any. I am RPMing those babies to death. For handgun bullets a general rule of thumb is that hard lubes are bad and soft lubes are good. Not all cases ............. but softer lubes would flow faster as they made more surface contact.
And as far as lube vaporizing, how IS lube used up? Ever watch a guy pushing his limits using the same lube as you? Almost all lubes smoke just before the end. And you match the viscosity of the lube to the pressure and conditions it must endure. Otherwise one super hard rifle lube should work under all conditions and NEVER break seal or lead at handgun velocities. You know no one lube fills all conditions.
The liquid theory supports seal, lubrication and changes in temperature or heat. Liquids boil off. The smaller the water drop the faster it heats and boils off. It can't boil off if it didn't absorb heat. That's where viscosity comes in. Racing cars have pistons and seals, but need heavier oil than passenger car engines not to break down huh? Just watch the Pennzoil commercial on TV. They talk about how their molecules recombine to counter shear forces and heat.
Remember, lead has a poor heat transfer rate, that's why it flash leads. There are two types of leading. Gas cutting and flash leading. Don't think so? How can you possibly have gas cutting in the taper of a taylor throat when that bullet is constantly sizing and getting smaller? You can't. Impossible! Especially at handgun pressures. That is frictional or flash leading. Gas cutting occurs after that. As a bullet begins to pass lead deposits, it has to size down. Once passed that point, there is your seal loss occurs. That is where gas cutting begins. BUT the cause was the flash or frictional leading.
But as far as mass goes with lead I believe it's insignificant because of the transfer rate problem. Only surface area and viscosity matters. And liquid lube will be covering that same area. If the viscosity matches the heat, it will endure, it will prevent friction, absorb the heat, and the seal will remain intact.
It has to, that's your seal.