It works well. The necks come out straight and we'll formed, once you get the pressure right. I use different powders and just stuff a pinch of cotton or even paper towel on top of the powder column, to hold the powder in place. You can control brass length with pressure. They will come out a few thou longer than expanding up with a mandrel, when the pressure is where you want it.It seems like this would work making 30BR brass as well. Have you tried going from 6mm to 30 cal using this method? How about you @Dusty Stevens
Way off topic. Apologies to the OP.