For small shells I shoot I have been having very good luck with a mix of my homade 20/60 mesh and rice hull powder seems to do exactly what you are speaking of for me. I'm changing out the 20/60M for 20/40 next to test the difference but I notice the rice hulls are very fast also. I cannot hear the difference very much but shells seem to go a lot higher with the rice hulls than without. I guess some more scientific testing is in order with an a stopwatch and some dummy loads.