One of the ultimate cases ever made is the
Kosdon 3" 10,000ns casing. From the numbers that I could come up
with, any propellant put in this case would become ignorant. So
for the first attempt, I chose a slow propellant, Renegade Red.
Burn time should be about 5 seconds, but with the erosiveness of the
propellant, I was figuring 3.5 seconds. It was even a bit shorter.