I believe the South Africans came up with a cooler burning propellant that lengthens barrel life, ie can take more firings until rebore.
Cooler burning = less energy. That’s what they had to use in Long Bertha in 1918 and still burned the 150+ caliber barrels like candles. There is only so much playing with the propellant grain shape one can do, while maintaining ballistic uniformity.