Rl-25 and RL-26 both seem to be less than ideal in that respect.
I'm still going to say that in order to change the powder burn, you have to heat or cool the powder or possibly primer not the barrel/action. There is some conduction from the barrel/action to the case, but for that to happen the round sit in the chamber for a while.
Similarly, barrel heading is done with waste heat after the burn. What happens to that heat has no impact on velocity.
