In my expereince W-231 burns more cleanly at the higher pressures of 9mm, 38 Super and 40 S&W. I have never had it burn clean for me in the lower pressure cartridges such as 38 Special or 45 ACP. I use W-231 for reloading medium velocity 38 Supers for my S&W 686 and it burns very clean with presuures in the 25000 psi range.